SWAKS(1) User Contributed Perl Documentation SWAKS(1)
Swaks - Swiss Army Knife SMTP, the all-purpose SMTP transaction tester
Swaks' primary design goal is to be a flexible, scriptable,
transaction-oriented SMTP test tool. It handles SMTP features and
extensions such as TLS, authentication, and pipelining; multiple
version of the SMTP protocol including SMTP, ESMTP, and LMTP; and
multiple transport methods including UNIX-domain sockets, internet-
domain sockets, and pipes to spawned processes. Options can be
specified in environment variables, configuration files, and the
command line allowing maximum configurability and ease of use for
operators and scripters.
Deliver a standard test email to email@example.com on port 25 of
swaks --to firstname.lastname@example.org --server test-server.example.net
Deliver a standard test email, requiring CRAM-MD5 authentication as
user email@example.com. An "X-Test" header will be added to the email
body. The authentication password will be prompted for.
swaks --to firstname.lastname@example.org --from email@example.com --auth CRAM-MD5 --auth-user firstname.lastname@example.org --header-X-Test "test email"
Test a virus scanner using EICAR in an attachment. Don't show the
message DATA part.:
swaks -t email@example.com --attach - --server test-server.example.com --suppress-data </path/to/eicar.txt
Test a spam scanner using GTUBE in the body of an email, routed via the
MX records for example.com:
swaks --to firstname.lastname@example.org --body /path/to/gtube/file
Deliver a standard test email to email@example.com using the LMTP
protocol via a UNIX domain socket file
swaks --to firstname.lastname@example.org --socket /var/lda.sock --protocol LMTP
Report all the recipients in a text file that are non-verifiable on a
for E in `cat /path/to/email/file`
swaks --to $E --server test-server.example.com --quit-after RCPT --hide-all
[ $? -ne 0 ] && echo $E
This document tries to be consistent and specific in its use of the
following terms to reduce confusion.
A transaction is the opening of a connection over a transport to a
target and using a messaging protocol to attempt to deliver a
The target of a transaction is the thing that Swaks connects to.
This generic term is used throughout the documentation because most
other terms improperly imply something about the transport being
The transport is the underlying method used to connect to the
The protocol is the application language used to communicate with
the target. This document uses SMTP to speak generically of all
three supported protocols unless it states that it is speaking of
the specific 'SMTP' protocol and excluding the others.
SMTP protocols exist to transfer messages, a set of bytes in an
agreed-upon format that has a sender and a recipient.
A message's envelope contains the "true" sender and receiver of a
message. It can also be referred to as its components, envelope-
sender and envelope-recipients. It is important to note that a
messages envelope does not have to match its To: and From: headers.
The DATA portion of an SMTP transaction is the actual message that
is being transported. It consists of both the message's headers
and its body. DATA and body are sometimes use synonymously, but
they are always two distinct things in this document.
A message's headers are defined as all the lines in the message's
DATA section before the first blank line. They contain information
about the email that will be displayed to the recipient such as
To:, From:, Subject:, etc. In this document headers will always be
written with a capitalized first letter and a trailing colon.
A message's body is the portion of its DATA section following the
first blank line.
To prevent potential confusion in this document a flag to Swaks is
always referred to as an "option". If the option takes additional
data, that additional data is referred to as an argument to the option.
For example, "--from email@example.com" might be provided to Swaks on
the command line, with "--from" being the option and "firstname.lastname@example.org"
being --from's argument.
Options can be given to Swaks in three ways. They can be specified in
a configuration file, in environment variables, and on the command
line. Depending on the specific option and whether an argument is
given to it, Swaks may prompt the user for the argument.
When Swaks evaluates its options, it first looks for a configuration
file (either in a default location or specified with --config). Then
it evaluates any options in environment variables. Finally, it
evaluates command line options. At each round of processing, any
options set earlier will be overridden. Additionally, any option can
be prefixed with "no-" to cause Swaks to forget that the variable had
previously been set (either in an earlier round, or earlier in the same
round). This capability is necessary because many options treat
defined-but-no-argument differently than not-defined.
As a general rule, if the same option is given multiple time, the last
time it is given is the one that will be used. This applies to both
intra-method (if "--from email@example.com --from firstname.lastname@example.org" is
given, email@example.com will be used) and inter-method (if "from
firstname.lastname@example.org" is given in a config file and "--from
email@example.com" is given on the command line, firstname.lastname@example.org will
The exact mechanism and format for using each of the types is listed
A configuration file can be used to set commonly-used or abnormally
verbose options. By default, Swaks looks in order for
$SWAKS_HOME/.swaksrc, $HOME/.swaksrc, and $LOGDIR/.swaksrc. If one
of those is found to exist (and --config has not been used) that
file is used as the configuration file.
Additionally, a configuration file in a non-default location can be
specified using --config. If this is set and not given an argument
Swaks will not use any configuration file, including any default
file. If --config points to a readable file, it is used as the
configuration file, overriding any default that may exist. If it
points to a non-readable file an error will be shown and Swaks will
A set of "portable" defaults can also be created by adding options
to the end of the Swaks program file. As distributed, the last
line of Swaks should be "__END__". Any lines added after __END__
will be treated as the contents of a configuration file. This
allows a set of user preferences to be automatically copied from
server to server in a single file.
If configuration files have not been explicitly turned off, the
__END__ config is always read. Only one other configuration file
will ever be used per single invocation of Swaks, even if multiple
configuration files are specified. If the __END__ config and
another config are to be read, the __END__ config will be processed
first. Specifying the --config option with no argument turns off
the processing of both the __END__ config and any actual config
In a configuration file lines beginning with a hash (#) are
ignored. All other lines are assumed to be an option to Swaks,
with the leading dash or dashes optional. Everything after a
option line's first space is assumed to be the option's argument
and is not shell processed. Therefore, quoting is usually unneeded
and will be included literally in the argument. Here is an example
of the contents of a configuration file:
# always use this sender, no matter server or logged in user
# I prefer my test emails have a pretty from header. Note
# the lack of dashes on option and lack of quotes around
# entire argument.
h-From: "Fred Example" <email@example.com>
Options specific to configuration file:
This option provides a path to a specific configuration file to
be used. If specified with no argument, no automatically-found
configuration file (via $HOME, etc, or __END__) will be
processed. If the argument is a valid file, that file will be
used as the configuration file (after __END__ config). If
option is not a valid, readable file, Swaks will error and
exit. This option can be specified multiple times, but only
the first time it is specified (in environment variable and the
command line search order) will be used.
Options can be supplied via environment variables. The variables
are in the form $SWAKS_OPT_name, where name is the name of the
option that would be specified on the command line. Because dashes
aren't allowed in environment variable names in most UNIX-ish
shells, no leading dashes should be used and any dashes inside the
option's name should be replaced with underscores. The following
would create the same options shown in the configuration file
$ SWAKS_OPT_h_From='"Fred Example" <firstname.lastname@example.org>'
Setting a variable to an empty value is the same as specifying it
on the command line with no argument. For instance, setting
SWAKS_OPT_server="" would cause Swaks to prompt the use for the
server to which to connect at each invocation.
Because there is no inherent order in options provided by setting
environment variables, the options are sorted before being
processed. This is not a great solution, but it at least defines
the behavior, which would be otherwise undefined. As an example,
if both SWAKS_OPT_from and SWAKS_OPT_f were set, the value from
SWAKS_OPT_from would be used, because it sorts after SWAKS_OPT_f.
Also as a result of not having an inherent order in environment
processing, unsetting options with the "no-" prefix is unreliable.
It works if the option being turned off sorts before "no-", but
fails if it sorts after. Because "no-" is primarily meant to
operate between config types (for instance, unsetting from the
command line an option that was set in a config file), this is not
likely to be a problem.
In addition to setting the equivalent of command line options,
SWAKS_HOME can be set to a directory containing the default
.swaksrc to be used.
COMMAND LINE OPTIONS
The final method of supplying options to Swaks is via the command
line. The options behave in a manner consistent with most UNIX-ish
command line programs. Many options have both a short and long
form (for instance -s and --server). By convention short options
are specified with a single dash and long options are specified
with a double-dash. This is only a convention and either prefix
will work with either type.
The following demonstrates the example shown in the configuration
file and environment variable sections:
$ swaks --from email@example.com --h-From: '"Fred Example" <firstname.lastname@example.org>'
Swaks can connect to a target via UNIX pipes ("pipes"), UNIX domain
sockets ("UNIX sockets"), or internet domain sockets ("network
sockets"). Connecting via network sockets is the default behavior.
Because of the singular nature of the transport used, each set of
options in the following section is mutually exclusive. Specifying
more than one of --server, --pipe, or --socket will result in an error.
Mixing other options between transport types will only result in the
irrelevant options being ignored. Below is a brief description of each
type of transport and the options that are specific to that transport
This transport attempts to deliver a message via TCP/IP, the
standard method for delivering SMTP. This is the default transport
for Swaks. If none of --server, --pipe, or --socket are given then
this transport is used and the target server is determined from the
recipient's domain (see --server below for more details).
This transport requires the IO::Socket module which is part of the
standard Perl distribution. If this module is not loadable,
attempting to use this transport will result in an error and
IPv6 is supported when the IO::Socket::INET6 module is present.
-s, --server [target mail server[:port]]
Explicitly tell Swaks to use network sockets and specify the
hostname or IP address to which to connect, or prompt if no
argument is given. If this option is not given and no other
transport option is given, the target mail server is determined
from the appropriate DNS records for the domain of the
recipient email address using the Net::DNS module. If Net::DNS
is not available Swaks will attempt to connect to localhost to
deliver. The target port can optionally be set here.
Supported formats for this include SERVER:PORT (supporting
names and IPv4 addresses); [SERVER]:PORT and SERVER/PORT
(supporting names, IPv4 and IPv6 addresses). See also
-p, --port [port]
Specify which TCP port on the target is to be used, or prompt
if no argument is listed. The argument can be a service name
(as retrieved by getservbyname(3)) or a port number. The
default port is smtp/25 unless influenced by the --protocol or
-li, --local-interface [IP or hostname[:port]]
Use argument as the local interface for the outgoing SMTP
connection, or prompt user if no argument given. Argument can
be an IP address or a hostname. Default action is to let the
operating system choose the local interface. See --server for
additional comments on :port format.
-lp, --local-port, --lport [port]
Specify the outgoing port to originate the transaction from.
If this option is not specified the system will pick an
ephemeral port. Note that regular users cannot specify some
The argument is interpreted as the domain part of an email
address and it is used to find the target server using the same
logic that would be used to look up the target server for a
recipient email address. See --to option for more details on
how the target is determined from the email domain.
Force IPv4 or IPv6.
This transport method attempts to deliver messages via a UNIX-
domain socket file. This is useful for testing MTA/MDAs that
listen on socket files (for instance, testing LMTP delivery to
Cyrus). This transport requires the IO::Socket module which is
part of the standard Perl distribution. If this module is not
loadable, attempting to use this transport will result in an error
and program termination.
This option takes as its argument a UNIX-domain socket file.
If Swaks is unable to open this socket it will display an error
This transport attempts to spawn a process and communicate with it
via pipes. The spawned program must be prepared to behave as a
mail server over STDIN/STDOUT. Any MTA designed to operate from
inet/xinet should support this. In addition, some MTAs provide
testing modes that can be communicated with via STDIN/STDOUT. This
transport can be used to automate that testing. For example, if
you implemented DNSBL checking with Exim and you wanted to make
sure it was working, you could run 'swaks --pipe "exim -bh
127.0.0.2"'. Ideally, the process you are talking to should behave
exactly like an SMTP server on STDIN and STDOUT. Any debugging
should be sent to STDERR, which will be directed to your terminal.
In practice, Swaks can generally handle some debug on the child's
STDOUT, but there are no guarantees on how much it can handle.
This transport requires the IPC::Open2 module which is part of the
standard Perl distribution. If this module is not loadable,
attempting to use this transport will result in an error and
--pipe [/path/to/command and arguments]
Provide a process name and arguments to the process. Swaks
will attempt to spawn the process and communicate with it via
pipes. If the argument is not an executable Swaks will display
an error and exit.
These options are related to the protocol layer.
-t, --to [email-address[,email-address,...]]
Tells Swaks to use argument(s) as the envelope-recipient for the
email, or prompt for recipient if no argument provided. If
multiple recipients are provided and the recipient domain is needed
to determine routing the domain of the last recipient provided is
There is no default value for this option. If no recipients are
provided via any means, user will be prompted to provide one
interactively. The only exception to this is if a --quit-after
value is provided which will cause the SMTP transaction to be
terminated before the recipient is needed.
-f, --from [email-address]
Use argument as envelope-sender for email, or prompt user if no
argument specified. The string <> can be supplied to mean the null
sender. If user does not specify a sender address a default value
is used. The domain-part of the default sender is a best guess at
the fully-qualified domain name of the local host. The method of
determining the local-part varies. On Windows, Win32::LoginName()
is used. On UNIX-ish platforms, the $LOGNAME environment variable
is used if it is set. Otherwise getpwuid(3) is used. See also
--force-getpwuid. If Swaks cannot determine a local hostname and
the sender address is needed for the transaction, Swaks will error
and exit. In this case, a valid string must be provided via this
--ehlo, --lhlo, -h, --helo [helo-string]
String to use as argument to HELO/EHLO/LHLO command, or prompt user
if no argument is specified. If this option is not used a best
guess at the fully-qualified domain name of the local host is used.
If Swaks cannot determine a local hostname and the helo string is
needed for the transaction, Swaks will error and exit. In this
case, a valid string must be provided via this option.
-q, --quit, --quit-after [stop-point]
Point at which the transaction should be stopped. When the
requested stopping point is reached in the transaction, and
provided that Swaks has not errored out prior to reaching it, Swaks
will send "QUIT" and attempt to close the connection cleanly.
These are the valid arguments and notes about their meaning.
Terminate the session after receiving the greeting banner from
FIRST-HELO, FIRST-EHLO, FIRST-LHLO
In a STARTTLS (but not tls-on-connect) session, terminate the
transaction after the first of two HELOs. In a non-STARTTLS
transaction, behaves the same as HELO (see below).
Quit after XCLIENT is sent.
Quit the transaction immediately following TLS negotiation.
Note that this happens in different places depending on whether
STARTTLS or tls-on-connect are used. This always quits after
the point where TLS would have been negotiated, regardless of
whether it was attempted.
HELO, EHLO, LHLO
In a STARTTLS or XCLIENT session, quit after the second HELO.
Otherwise quit after the first and only HELO.
Quit after authentication. This always quits after the point
where authentication would have been negotiated, regardless of
whether it was attempted.
Quit after MAIL FROM: is sent.
Quit after RCPT TO: is sent.
--da, --drop-after [stop-point]
The option is similar to --quit-after, but instead of trying to
cleanly shut down the session it simply terminates the session.
This option accepts the same stop-points as --quit-after and
additionally accepts DATA and DOT, detailed below.
Quit after DATA is sent.
DOT Quit after the final '.' of the message is sent.
--das, --drop-after-send [stop-point]
This option is similar to --drop-after, but instead of dropping the
connection after reading a response to the stop-point, it drops the
connection immediately after sending stop-point. It accepts the
same stop-points as --drop-after.
Use argument as the SMTP transaction timeout, or prompt user if no
argument given. Argument can either be a pure digit, which will be
interpreted as seconds, or can have a specifier s or m (5s = 5
seconds, 3m = 180 seconds). As a special case, 0 means don't
timeout the transactions. Default value is 30s.
Specify which protocol to use in the transaction. Valid options
are shown in the table below. Currently the 'core' protocols are
SMTP, ESMTP, and LMTP. By using variations of these protocol types
one can tersely specify default ports, whether authentication
should be attempted, and the type of TLS connection that should be
attempted. The default protocol is ESMTP. This table demonstrates
the available arguments to --protocol and the options each sets as
a side effect:
HELO, "-p 25"
EHLO->HELO, "-tlsc -p 465"
EHLO->HELO, "-a -tlsc -p 465"
HELO, "-tlsc -p 465"
EHLO->HELO, "-p 25"
EHLO->HELO, "-a -p 25"
EHLO->HELO, "-tls -p 25"
EHLO->HELO, "-a -tls -p 25"
LHLO, "-p 24"
LHLO, "-a -p 24"
LHLO, "-tls -p 24"
LHLO, "-a -tls -p 24"
If the remote server supports it, attempt SMTP PIPELINING (RFC
If the server supports it, attempt Per-Recipient Data Response
(PRDR) (https://tools.ietf.org/html/draft-hall-prdr-00.txt). PRDR
is not yet standardized, but MTAs have begun implementing the
Tell Swaks to use the getpwuid method of finding the default sender
local-part instead of trying $LOGNAME first.
These are options related to encrypting the transaction. These have
been tested and confirmed to work with all three transport methods.
The Net::SSLeay module is used to perform encryption when it is
requested. If this module is not loadable Swaks will either ignore the
TLS request or error out, depending on whether the request was
optional. STARTTLS is defined as an extension in the ESMTP protocol
and will be unavailable if --protocol is set to a variation of SMTP.
Because it is not defined in the protocol itself, --tls-on-connect is
available for any protocol type if the target supports it.
A local certificate is not required for a TLS connection to be
negotiated. However, some servers use client certificate checking to
verify that the client is allowed to connect. Swaks can be told to use
a specific local certificate using the --tls-cert and --tls-key
Require connection to use STARTTLS. Exit if TLS not available for
any reason (not advertised, negotiations failed, etc).
Attempt to use STARTTLS if available, continue with normal
transaction if TLS was unable to be negotiated for any reason.
Note that this is a semi-useless option as currently implemented
because after a negotiation failure the state of the connection is
unknown. In some cases, like a version mismatch, the connection
should be left as plaintext. In others, like a verification
failure, the server-side may think that it should continue speaking
TLS while the client thinks it is plaintext. There may be an
attempt to add more granular state detection in the future, but for
now just be aware that odd things may happen with this option if
the TLS negotiation is attempted and fails.
Attempt to use STARTTLS if available. Proceed with transaction if
TLS is negotiated successfully or STARTTLS not advertised. If
STARTTLS is advertised but TLS negotiations fail, treat as an error
and abort transaction. Due to the caveat noted above, this is a
much saner option than --tls-optional.
Initiate a TLS connection immediately on connection. Following
common convention, if this option is specified the default port
changes from 25 to 465, though this can still be overridden with
the --port option.
-tlsp, --tls-protocol SPECIFICATION
Specify which protocols to use (or not use) when negotiating TLS.
At the time of this writing, the available protocols are sslv2,
sslv3, tlsv1, tlsv1_1, tlsv1_2, and tlsv1_3. The availability of
these protocols is dependent on your underlying OpenSSL library, so
not all of these may be available. The list of available protocols
is shown in the output of --dump (assuming TLS is available at
The specification string is a comma-delimited list of protocols
that can be used or not used. For instance 'tlsv1,tlsv1_1' will
only succeed if one of those two protocols is available on both the
client and the server. Conversely, 'no_sslv2,no_sslv3' will
attempt to negotiate any protocol except sslv2 and sslv3. The two
forms of specification cannot be mixed.
The argument to this option is passed to the underlying OpenSSL
library to set the list of acceptable ciphers to the be used for
the connection. The format of this string is opaque to Swaks and
is defined in
A brief example would be --tls-cipher '3DES:+RSA'.
Tell Swaks to attempt to verify the server's certificate. If this
option is set and the server's certificate is not verifiable
(either using the system-default CA information, or custom CA
information (see --tls-ca-path)) TLS negotiation will not succeed.
By default, Swaks does not attempt certificate verification.
--tls-ca-path [ /path/to/CAfile | /path/to/CAdir/ ]
Specify an alternate location for CA information for verifying
server certificates. The default behavior is to use the underlying
OpenSSL library's default information.
Provide a path to a file containing the local certificate Swaks
should use if TLS is negotiated. The file path argument is
required. As currently implemented the certificate in the file
must be in PEM format. Contact the author if there's a compelling
need for ASN1. If this option is set, --tls-key is also required.
Provide a path to a file containing the local private key Swaks
should use if TLS is negotiated. The file path argument is
required. As currently implemented the certificate in the file
must be in PEM format. Contact the author if there's a compelling
need for ASN1. If this option is set, --tls-cert is also required.
Get a copy of the TLS peer's certificate. If no argument is given,
it will be displayed to STDOUT. If an argument is given it is
assumed to be a filesystem path specifying where the certificate
should be written. The saved certificate can then be examined
using standard tools such as the openssl command. If a file is
specified its contents will be overwritten.
Swaks will attempt to authenticate to the target mail server if
instructed to do so. This section details available authentication
types, requirements, options and their interactions, and other fine
points in authentication usage. Because authentication is defined as
an extension in the ESMTP protocol it will be unavailable if --protocol
is set to a variation of SMTP.
All authentication methods require base64 encoding. If the
MIME::Base64 Perl module is loadable Swaks attempts to use it to
perform these encodings. If MIME::Base64 is not available Swaks will
use its own onboard base64 routines. These are slower than the
MIME::Base64 routines and less reviewed, though they have been tested
thoroughly. Using the MIME::Base64 module is encouraged.
If authentication is required (see options below for when it is and
isn't required) and the requirements aren't met for the authentication
type available, Swaks displays an error and exits. Two ways this can
happen include forcing Swaks to use a specific authentication type that
Swaks can't use due to missing requirements, or allowing Swaks to use
any authentication type, but the server only advertises types Swaks
can't support. In the former case Swaks errors out at option
processing time since it knows up front it won't be able to
authenticate. In the latter case Swaks will error out at the
authentication stage of the SMTP transaction since Swaks will not be
aware that it will not be able to authenticate until that point.
Following are the supported authentication types including any
individual notes and requirements.
The following options affect Swaks' use of authentication. These
options are all inter-related. For instance, specifying --auth-user
implies --auth and --auth-password. Specifying --auth-optional implies
--auth-user and --auth-password, etc.
-a, --auth [auth-type[,auth-type,...]]
Require Swaks to authenticate. If no argument is given, any
supported auth-types advertised by the server are tried until one
succeeds or all fail. If one or more auth-types are specified as
an argument, each that the server also supports is tried in order
until one succeeds or all fail. This option requires Swaks to
authenticate, so if no common auth-types are found or no
credentials succeed, Swaks displays an error and exits.
The following tables lists the valid auth-types
These basic authentication types are fully supported and tested
and have no additional requirements
The CRAM-MD5 authenticator requires the Digest::MD5 module. It
is fully tested and believed to work against any server that
The DIGEST-MD5 authenticator (RFC2831) requires the
Authen::SASL module. Version 20100211.0 and earlier used
Authen::DigestMD5 which had some protocol level errors which
prevented it from working with some servers. Authen::SASL's
DIGEST-MD5 handling is much more robust.
The DIGEST-MD5 implementation in Swaks is fairly immature. It
currently supports only the "auth" qop type, for instance. If
you have DIGEST-MD5 experience and would like to help Swaks
support DIGEST-MD5 better, please get in touch with me.
The DIGEST-MD5 protocol's "realm" value can be set using the
--auth-extra "realm" keyword. If no realm is given, a
reasonable default will be used.
The DIGEST-MD5 protocol's "digest-uri" values can be set using
the --auth-extra option. For instance, you could create the
digest-uri-value of "lmtp/mail.example.com/example.com" with
the option "--auth-extra
The "digest-uri-value" string and its components is defined in
RFC2831. If none of these values are given, reasonable
defaults will be used.
The CRAM-SHA1 authenticator requires the Digest::SHA module.
This type has only been tested against a non-standard
implementation on an Exim server and may therefore have some
These authenticators require the Authen::NTLM module. Note
that there are two modules using the Authen::NTLM namespace on
CPAN. The Mark Bush implementation (Authen/NTLM-1.03.tar.gz)
is the version required by Swaks. This type has been tested
against Exim, Communigate, and Exchange 2007.
In addition to the standard username and password, this
authentication type can also recognize a "domain". The domain
can be set using the --auth-extra "domain" keyword. Note that
this has never been tested with a mail server that doesn't
ignore DOMAIN so this may be implemented incorrectly.
-ao, --auth-optional [auth-type[,auth-type,...]]
This option behaves identically to --auth except that it requests
authentication rather than requiring it. If no common auth-types
are found or no credentials succeed, Swaks proceeds as if
authentication had not been requested.
-aos, --auth-optional-strict [auth-type[,auth-type,...]]
This option is a compromise between --auth and --auth-optional. If
no common auth-types are found, Swaks behaves as if --auth-optional
were specified and proceeds with the transaction. If Swaks can't
support requested auth-type, the server doesn't advertise any
common auth-types, or if no credentials succeed, Swaks behaves as
if --auth were used and exits with an error.
-au, --auth-user [username]
Provide the username to be used for authentication, or prompt the
user for it if no argument is provided. The string <> can be
supplied to mean an empty username.
-ap, --auth-password [password]
Provide the password to be used for authentication, or prompt the
user for it if no argument is provided. The string <> can be
supplied to mean an empty password.
-ae, --auth-extra [KEYWORD=value[,...]]
Some of the authentication types allow extra information to be
included in the authentication process. Rather than add a new
option for every nook and cranny of each authenticator, the
--auth-extra option allows this information to be supplied.
The following table lists the currently recognized keywords and the
authenticators that use them
The realm and domain keywords are synonymous. Using either
will set the "domain" option in NTLM/MSN/SPA and the "realm"
option in DIGEST-MD5
The dmd5-serv-type keyword is used by the DIGEST-MD5
authenticator and is used, in part, to build the digest-uri-
value string (see RFC2831)
The dmd5-host keyword is used by the DIGEST-MD5 authenticator
and is used, in part, to build the digest-uri-value string (see
The dmd5-serv-name keyword is used by the DIGEST-MD5
authenticator and is used, in part, to build the digest-uri-
value string (see RFC2831)
-am, --auth-map [auth-alias=auth-type[,...]]
Provides a way to map alternate names onto base authentication
types. Useful for any sites that use alternate names for common
types. This functionality is actually used internally to map types
SPA and MSN onto the base type NTLM. The command line argument to
simulate this would be "--auth-map SPA=NTLM,MSN=NTLM". All of the
auth-types listed above are valid targets for mapping except SPA
Instead of showing AUTH strings base64 encoded as they are
transmitted, translate them to plaintext before printing on screen.
-ahp, --auth-hide-password [replacement string]
If this option is specified, any time a readable password would be
printed to the terminal (specifically AUTH PLAIN and AUTH LOGIN)
the password is replaced with the string 'PROVIDED_BUT_REMOVED' (or
the contents of "replacement string" if provided). The dummy
string may or may not be base64 encoded, contingent on the
Note that --auth-hide-password is similar, but not identical, to
the --protect-prompt option. The former protects passwords from
being displayed in the SMTP transaction regardless of how they are
entered. The latter protects sensitive strings when the user types
them at the terminal, regardless of how the string would be used.
XCLIENT is an SMTP extension introduced by the Postfix project.
XCLIENT allows a (properly-authorized) client to tell a server to use
alternate information, such as IP address or hostname, for the client.
This allows much easier paths for testing mail server configurations.
Full details on the protocol are available at
The XCLIENT verb can be passed to the server multiple times per SMTP
session with different attributes. For instance, HELO and PROTO might
be passed in one call and NAME and ADDR passed in a second. Because it
can be useful for testing, Swaks exposes some control over how the
attributes are grouped and in what order they are passed to the server.
The different options attempt to expose simplicity for those using
Swaks as a client, and complexity for those using Swaks to test
These options specify XCLIENT attributes that should be sent to the
target server. If [VALUE] is not provided, Swaks will prompt and
read the value on STDIN. See
http://www.postfix.org/XCLIENT_README.html for official
documentation for what the attributes mean and their possible
values, including the special "[UNAVAILABLE]" and "[TEMPUNAVAIL]"
By way of simple example, setting "--xclient-name foo.example.com
--xclient-addr 192.168.1.1" will cause Swaks to send the SMTP
command "XCLIENT NAME=foo.example.com ADDR=192.168.1.1".
Note that the "REVERSE_NAME" attribute doesn't seem to appear in
the official documentation. There is a mailing list thread that
documents it, viewable at
These options can all be mixed with each other, and can be mixed
with the --xclient option (see below). By default all attributes
will be combined into one XCLIENT call, but see --xclient-delim.
When this option is specified, it indicates a break in XCLIENT
attributes to be sent. For instance, setting "--xclient-helo 'helo
string' --xclient-delim --xclient-name foo.example.com
--xclient-addr 192.168.1.1" will cause Swaks to send two XCLIENT
calls, "XCLIENT HELO=helo+20string" and "XCLIENT
NAME=foo.example.com ADDR=192.168.1.1". This option is ignored
where it doesn't make sense (at the start or end of XCLIENT
options, by itself, consecutively, etc).
This is the "free form" XCLIENT option. Whatever value is provided
for XCLIENT_STRING will be sent verbatim as the argument to the
XCLIENT SMTP command. For example, if "--xclient 'NAME=
ADDR=192.168.1.1 FOO=bar'" is used, Swaks will send the SMTP
command "XCLIENT NAME= ADDR=192.168.1.1 FOO=bar". If no
XCLIENT_STRING is passed on command line, Swaks will prompt and
read the value on STDIN.
The primary advantage to this over the more specific options above
is that there is no XCLIENT syntax validation here. This allows
you to send invalid XCLIENT to the target server for testing.
Additionally, at least one MTA (Message Systems' Momentum, formerly
ecelerity) implements XCLIENT without advertising supported
attributes. The --xclient option allows you to skip the "supported
attributes" check when communicating with this type of MTA (though
see also --xclient-no-verify).
The --xclient option can be mixed freely with the --xclient-*
options above. The argument to --xclient will be sent in its own
command group. For instance, if "--xclient-addr 192.168.0.1
--xclient-port 26 --xclient 'FOO=bar NAME=wind'" is given to Swaks,
"XCLIENT ADDR=192.168.0.1 PORT=26" and "XCLIENT FOO=bar NAME=wind"
will both be sent to the target server.
Do not enforce the requirement that an XCLIENT attribute must be
advertised by the server in order for Swaks to send it in an
XCLIENT command. This is to support servers which don't advertise
the attributes but still support them.
If Swaks is configured to attempt both XCLIENT and STARTTLS, it
will do STARTTLS first. If this option is specified it will
attempt XCLIENT first.
In normal operation, setting one of the --xclient* options will
require a successful XCLIENT transaction to take place in order to
proceed (that is, XCLIENT needs to be advertised, all the user-
requested attributes need to have been advertised, and the server
needs to have accepted Swaks' XCLIENT request). These options
change that behavior. --xclient-optional tells Swaks to proceed
unconditionally past the XCLIENT stage of the SMTP transaction,
regardless of whether it was successful. --xclient-optional-strict
is similar but more granular. The strict version will continue to
XCLIENT was not advertised, but will fail if XCLIENT was attempted
but did not succeed.
Swaks implements the Proxy protocol as defined in
allows an application load balancer, such as HAProxy, to be used in
front of an MTA while still allowing the MTA access to the originating
host information. Proxy support in Swaks allows direct testing of an
MTA configured to expect requests from a proxy, bypassing the proxy
itself during testing.
Swaks makes no effort to ensure that the Proxy options used are
internally consistent. For instance, --proxy-family (in version 1) is
expected to be one of "TCP4" or "TCP6". While it will likely not make
sense to the target server, Swaks makes no attempt to ensure that
--proxy-source and --proxy-dest are in the same protocol family as
--proxy-family or each other.
The --proxy option is mutually exclusive with all other --proxy-*
options except --proxy-version.
When --proxy is not used, all of --proxy-family, --proxy-source,
--proxy-source-port, --proxy-dest, and --proxy-dest-port are required.
Additionally, when --proxy-version is 2, --proxy-protocol and
--proxy-command are optional.
--proxy-version [ 1 | 2 ]
Whether to use version 1 (human readable) or version 2 (binary) of
the Proxy protocol. Version 1 is the default. Version 2 is only
implemented through the "address block", and is roughly on par with
the information provided in version 1.
If this option is used, its argument is passed unchanged after the
"PROXY " portion (or the 12-byte protocol header for version 2) of
the Proxy exchange. This option allows sending incomplete or
malformed Proxy strings to a target server for testing. No attempt
to translate or modify this string is made, so if used with
"--proxy-version 2" the argument should be in the appropriate
binary format. This option is mutually exclusive with all other
--proxy-* options which provide granular proxy information.
For version 1, specifies both the address family and transport
protocol. The protocol defines TCP4 and TCP6.
For version 2, specifies only the address family. The protocol
defines AF_UNSPEC, AF_INET, AF_INET6, and AF_UNIX.
For version 2, specifies the transport protocol. The protocol
defines UNSPEC, STREAM, and DGRAM. The default is STREAM. This
option is unused in version 1
For version 2, specifies the transport protocol. The protocol
defines LOCAL and PROXY. The default is PROXY. This option is
unused in version 1
Specify the source address of the proxied connection.
Specify the source port of the proxied connection.
Specify the destination address of the proxied connection.
Specify the destination port of the proxied connection.
These options pertain to the contents for the DATA portion of the SMTP
transaction. By default a very simple message is sent. If the
--attach or --attach-body options are used, Swaks attempts to upgrade
to a MIME message.
-d, --data [data-portion]
Use argument as the entire contents of DATA.
If no argument is provided, user will be prompted to supply value.
If the argument '-' is provided the data will be read from STDIN
with no prompt (same as -g).
If the argument does not contain any literal (0x0a) or
representative (0x5c, 0x6e or %NEWLINE%) newline characters, it
will be treated as a filename. If the file is open-able, the
contents of the file will be used as the data portion. If the file
cannot be opened, Swaks will error and exit.
Any other argument will be used as the DATA contents.
The value can be on one single line, with \n (ASCII 0x5c, 0x6e)
representing where line breaks should be placed. Leading dots will
be quoted. Closing dot is not required but is allowed. The
default value for this option is "Date: %DATE%\nTo:
%TO_ADDRESS%\nFrom: %FROM_ADDRESS%\nSubject: test
%DATE%\nMessage-Id: <%MESSAGEID%>\nX-Mailer: swaks v%SWAKS_VERSION%
Very basic token parsing is performed on the DATA portion. The
following table shows the recognized tokens and their replacement
Replaced with the envelope-sender.
Replaced with the envelope-recipient(s).
Replaced with the current time in a format suitable for
inclusion in the Date: header. Note this attempts to use the
standard module Time::Local for timezone calculations. If this
module is unavailable the date string will be in GMT.
Replaced with a message ID string suitable for use in a
Message-Id header. The value for this token will remain
consistent for the life of the process.
Replaced with the version of the currently-running Swaks
Replaced with the contents of the --add-header option. If
--add-header is not specified this token is simply removed.
Replaced with the value specified by the --body option. See
--body for default.
Replaced with carriage return, newline (0x0d, 0x0a). This is
identical to using '\n' (0x5c, 0x6e), but doesn't have the
escaping concerns that the backslash can cause on the newline.
-dab, --dump-as-body [section[,section]]
If --dump-as-body is used and no other option is used to change the
default body of the message, the body is replaced with output
similar to the output of what is provided by --dump. --dump's
initial program capability stanza is not displayed, and the "data"
section is not included. Additionally, --dump always includes
passwords. By default --dump-as-body does not include passwords,
though this can be changed with --dump-as-body-shows-password.
--dump-as-body takes the same arguments as --dump except the
SUPPORT and DATA arguments are not supported.
Cause --dump-as-body to include plaintext passwords. This option
is not recommended. This option implies --dump-as-body.
Specify the body of the email. The default is "This is a test
mailing". If no argument to --body is given, prompt to supply one
interactively. If '-' is supplied, the body will be read from
standard input. If any other text is provided and the text
represents an open-able file, the content of that file is used as
the body. If it does not represent an open-able file, the text
itself is used as the body.
If the message is forced to MIME format (see --attach) "--body
'body text'" is the same as "--attach-type text/plain --attach-body
'body text'". See --attach-body for details on creating a
When one or more --attach option is supplied, the message is
changed into a multipart/mixed MIME message. The arguments to
--attach are processed the same as --body with respect to STDIN,
file contents, etc. --attach can be supplied multiple times to
create multiple attachments. By default, each attachment is
attached as an application/octet-stream file. See --attach-type
for changing this behavior.
If the contents of the attachment are provided via a file name, the
MIME encoding will include that file name. See --attach-name for
more detail on file naming.
It is legal for '-' (STDIN) to be specified as an argument multiple
times (once for --body and multiple times for --attach). In this
case, the same content will be attached each time it is specified.
This is useful for attaching the same content with multiple MIME
This is a variation on --attach that is specifically for the body
part of the email. It behaves identically to --attach in that it
takes the same arguments and forces the creation of a MIME message.
However, it is different in that the argument will always be the
first MIME part in the message, no matter where in option
processing order it is encountered. Additionally, --attach-body
options stack to allow creation of multipart/alternative bodies.
For example, '--attach-type text/plain --attach "plain text body"
--attach-type text/html --attach "html body"' would create a
multipart/alternative message body.
By default, content that gets MIME attached to a message with the
--attach option is encoded as application/octet-stream (except for
the body, which is text/plain by default). --attach-type changes
the mime type for every --attach option which follows it. It can
be specified multiple times. The current MIME type gets reset to
application/octet-stream between processing body parts and other
This option sets the filename that will be included in the MIME
part created for the next --attach option. If no argument is set
for this option, it causes no filename information to be included
for the next MIME part, even if Swaks could generate it from the
local file name.
-ah, --add-header [header]
This option allows headers to be added to the DATA. If
%NEW_HEADERS% is present in the DATA it is replaced with the
argument to this option. If %NEW_HEADERS% is not present, the
argument is inserted between the first two consecutive newlines in
the DATA (that is, it is inserted at the end of the existing
The option can either be specified multiple times or a single time
with multiple headers separated by a literal '\n' string. So,
"--add-header 'Foo: bar' --add-header 'Baz: foo'" and "--add-header
'Foo: bar\nBaz: foo'" end up adding the same two headers.
--header [header-and-data], --h-Header [data]
These options allow a way to change headers that already exist in
the DATA. '--header "Subject: foo"' and '--h-Subject foo' are
equivalent. If the header does not already exist in the data then
this argument behaves identically to --add-header. However, if the
header already exists it is replaced with the one specified.
-g If specified, Swaks will read the DATA value for the mail from
STDIN. This is equivalent to "--data -". If there is a From_ line
in the email, it will be removed (but see -nsf option). Useful for
delivering real message (stored in files) instead of using example
This option forces Swaks to do no massaging of the DATA portion of
the email. This includes token replacement, From_ stripping,
trailing-dot addition, --body/attachment inclusion, and any header
additions. This option is only useful when used with --data, since
the internal default DATA portion uses tokens.
Don't strip the From_ line from the DATA portion, if present.
Swaks provides a transcript of its transactions to its caller
(STDOUT/STDERR) by default. This transcript aims to be as faithful a
representation as possible of the transaction though it does modify
this output by adding informational prefixes to lines and by providing
plaintext versions of TLS transactions
The "informational prefixes" are referred to as transaction hints.
These hints are initially composed of those marking lines that are
output of Swaks itself, either informational or error messages, and
those that indicate a line of data actually sent or received in a
transaction. This table indicates the hints and their meanings:
Indicates an informational line generated by Swaks
Indicates an error generated within Swaks
Indicates an expected line sent by Swaks to target server
Indicates a TLS-encrypted, expected line sent by Swaks to target
Indicates an unexpected line sent by Swaks to the target server
Indicates a TLS-encrypted, unexpected line sent by Swaks to target
Indicates a raw chunk of text sent by Swaks to a target server (see
--show-raw-text). There is no concept of "expected" or
"unexpected" at this level.
Indicates an expected line sent by target server to Swaks
Indicates a TLS-encrypted, expected line sent by target server to
Indicates an unexpected line sent by target server to Swaks
Indicates a TLS-encrypted, unexpected line sent by target server to
Indicates a raw chunk of text received by Swaks from a target
server (see --show-raw-text). There is no concept of "expected" or
"unexpected" at this level.
The following options control what and how output is displayed to the
Summarizes the DATA portion of the SMTP transaction instead of
printing every line. This option is very helpful, bordering on
required, when using Swaks to send certain test emails. Emails
with attachments, for instance, will quickly overwhelm a terminal
if the DATA is not suppressed.
-stl, --show-time-lapse [i]
Display time lapse between send/receive pairs. This option is most
useful when Time::HiRes is available, in which case the time lapse
will be displayed in thousandths of a second. If Time::HiRes is
unavailable or "i" is given as an argument the lapse will be
displayed in integer seconds only.
Don't display the transaction hint for informational transactions.
This is most useful when needing to copy some portion of the
informational lines, for instance the certificate output from
--no-send-hints and --no-receive-hints suppress the transaction
prefix from send and receive lines, respectively. This is often
useful when copying some portion of the transaction for use
elsewhere (for instance, "--no-send-hints --hide-receive
--hide-informational" is a useful way to get only the client-side
commands for a given transaction). --no-hints is identical to
specifying both --no-send-hints and --no-receive-hints.
Don't show transaction hints (useful in conjunction with -hr to
create copy/paste-able transactions).
This option will print a hex dump of raw data sent and received by
Swaks. Each hex dump is the contents of a single read or write on
the network. This should be identical to what is already being
displayed (with the exception of the \r characters being removed).
This option is useful in seeing details when servers are sending
lots of data in single packets, or breaking up individual lines
into multiple packets. If you really need to go in depth in that
area you're probably better with a packet sniffer, but this option
is a good first step to seeing odd connection issues.
--output, --output-file </path/to/file>
These options allow the user to send output to files instead of
STDOUT/STDERR. The first option sends both to the same file. The
arguments of &STDOUT and &STDERR are treated specially, referring
to the "normal" file handles, so "--output-file-stderr '&STDOUT'"
would redirect STDERR to STDOUT. These options are honored for all
output except --help and --version.
Don't echo user input on prompts that are potentially sensitive
(right now only authentication password). See also
Don't display lines sent from the remote server being received by
Don't display lines being sent by Swaks to the remote server
Don't display non-error informational lines from Swaks itself.
Do not display any content to the terminal.
-S, --silent [level]
Cause Swaks to be silent. If no argument is given or if an
argument of "1" is given, print no output unless/until an error
occurs, after which all output is shown. If an argument of "2" is
given, only print errors. If "3" is given, show no output ever.
--silent affects most output but not all. For instance, --help,
--version, --dump, and --dump-mail are not affected.
Print capabilities and exit. Certain features require non-standard
Perl modules. This option evaluates whether these modules are
present and displays which functionality is available and which
isn't, and which modules would need to be added to gain the missing
Cause Swaks to process all options to generate the message it would
send, then print that message to STDOUT instead of sending it.
This output is identical to the "data" section of --dump, except
without the trailing dot.
This option causes Swaks to print the results of option processing,
immediately before mail would have been sent. No mail will be sent
when --dump is used. Note that --dump is a pure self-diagnosis
tool and no effort is made or will ever be made to mask passwords
in the --dump output. If a section is provided as an argument to
this option, only the requested section will be shown. Currently
supported arguments are SUPPORT, APP, OUTPUT, TRANSPORT, PROTOCOL,
XCLIENT, PROXY, TLS, AUTH, DATA, and ALL. If no argument is
provided, all sections are displayed
Display this help information and exit.
Display version information and exit.
This program was primarily intended for use on UNIX-like operating
systems, and it should work on any reasonable version thereof. It
has been developed and tested on Solaris, Linux, and Mac OS X and
is feature complete on all of these.
This program is known to demonstrate basic functionality on Windows
using ActiveState's Perl. It has not been fully tested. Known to
work are basic SMTP functionality and the LOGIN, PLAIN, and
CRAM-MD5 auth types. Unknown is any TLS functionality and the
NTLM/SPA and DIGEST-MD5 auth types.
Because this program should work anywhere Perl works, I would
appreciate knowing about any new operating systems you've
thoroughly used Swaks on as well as any problems encountered on a
This program was almost exclusively developed against Exim mail
servers. It has been used casually by the author, though not
thoroughly tested, with Sendmail, Smail, Exchange, Oracle
Collaboration Suite, qpsmtpd, and Communigate. Because all
functionality in Swaks is based on known standards it should work
with any fairly modern mail server. If a problem is found, please
alert the author at the address below.
If Swaks must create a sender address, $LOGNAME is used as the
message local-part if it is set, and unless --force-getpwuid is
Used when searching for a .swaksrc configuration file. See OPTION
PROCESSING -> CONFIGURATION FILES above.
Environment variable prefix used to specify Swaks options from
environment variables. See OPTION PROCESSING -> ENVIRONMENT
0 no errors occurred
1 error parsing command line options
2 error connecting to remote server
3 unknown connection type
4 while running with connection type of "pipe", fatal problem writing
to or reading from the child process
5 while running with connection type of "pipe", child process died
unexpectedly. This can mean that the program specified with --pipe
6 Connection closed unexpectedly. If the close is detected in
response to the 'QUIT' Swaks sends following an unexpected
response, the error code for that unexpected response is used
instead. For instance, if a mail server returns a 550 response to
a MAIL FROM: and then immediately closes the connection, Swaks
detects that the connection is closed, but uses the more specific
exit code 23 to detail the nature of the failure. If instead the
server return a 250 code and then immediately closes the
connection, Swaks will use the exit code 6 because there is not a
more specific exit code.
10 error in prerequisites (needed module not available)
21 error reading initial banner from server
22 error in HELO transaction
23 error in MAIL transaction
24 no RCPTs accepted
25 server returned error to DATA request
26 server did not accept mail following data
27 server returned error after normal-session quit request
28 error in AUTH transaction
29 error in TLS transaction
30 PRDR requested/required but not advertised
32 error in EHLO following TLS negotiation
33 error in XCLIENT transaction
34 error in EHLO following XCLIENT
35 error in PROXY option processing
36 error sending PROXY banner
The name "Swaks" is a (sort-of) acronym for "SWiss Army Knife SMTP".
It was chosen to be fairly distinct and pronounceable. While "Swaks"
is unique as the name of a software package, it has some other, non-
software meanings. Please send in other uses of "swak" or "swaks" for
"Sealed With A Kiss"
SWAK/SWAKs turns up occasionally on the internet with the meaning
bad / poor / ill (Afrikaans)
Seen in the headline "SA se bes en swaks gekledes in 2011", which
was translated as "best and worst dressed" by native speakers.
Google Translate doesn't like "swaks gekledes", but it will
translate "swak" as "poor" and "swak geklede" as "ill-dressed".
This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2 of the License, or (at your
option) any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
General contact, questions, patches, requests, etc to
Change logs, this help, and the latest version are found at
Swaks is crafted with love by John Jetmore from the cornfields of
Indiana, United States of America.
If you would like to be put on a list to receive notifications when
a new version of Swaks is released, please send an email to this
address. There will not be a response to your email.
perl v5.30.1 2020-01-31 SWAKS(1)