1MSMTPD(1) General Commands Manual MSMTPD(1)
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6 msmtpd - A minimal SMTP server
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9 msmtpd [option...]
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12 Msmtpd is a minimal SMTP server that pipes mails to msmtp (or some
13 other program) for delivery. It can be used with system services that
14 expect an SMTP server on the local host, or it can be used by end users
15 as a way to handle outgoing mail via msmtp with mail clients that in‐
16 sist on using SMTP. The EXAMPLES section below contains examples for
17 both use cases.
18 Msmtpd listens on 127.0.0.1 port 25 by default, but can also run with‐
19 out its own network sockets in inetd mode, where it handles a single
20 SMTP session on standard input / output.
21 In the string that defines the command that msmtpd pipes each mail to,
22 the first occurrence of %F will be replaced with the envelope from ad‐
23 dress. Furthermore, all recipients of the mail will be appended as ar‐
24 guments. The command must not write to standard output, as that would
25 mess up the SMTP session.
26 If the command that the mail is piped to reports an error, this is typ‐
27 ically reported as a permanent failure by msmtpd (SMTP server return
28 code 554). The command can optionally signal temporary errors by using
29 return codes defined in sysexits.h, e.g. 75 for EX_TEMPFAIL. These will
30 then be reported as temporary failures by msmtpd (SMTP server return
31 code 451), which means the client should try again later.
32 To prevent abuse, msmtpd will allow only a limited number of concurrent
33 SMTP sessions, and if authentication is active and an authentication
34 failure occurrs, future authentication requests in any SMTP session
35 will (for a limited duration) only be answered after a small delay.
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38 --version
39 Print version information
40 --help Print help
42 --inetd
44 Start single SMTP session on stdin/stdout
45 --interface=ip
47 Listen on the given IPv6 or IPv4 address instead of 127.0.0.1
48 --port=number
50 Listen on the given port number instead of 25
51 --log=none|syslog|filename
53 Set logging: none (default), syslog, or logging to the given
54 file.
55 --command=cmd
57 Pipe mails to cmd instead of msmtp. Make sure to end this com‐
58 mand with -- to separate options from arguments.
59 --auth=user[,passwordeval]
61 Require authentication with this user name. The password will be
62 retrieved from the given passwordeval command (this works just
63 like passwordeval in msmtp) or, if none is given, from the key
64 ring or, if that fails, from a prompt.
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67 Using msmtpd as a system service
68 Only use a local interface to listen on. Run msmtpd with correct user
69 rights and permissions (e.g. use CAP_NET_BIND_SERVICE to bind to port
70 25 instead of running as root, or use systemd with inetd service capa‐
71 bilities). Be aware that the pipe command will be run as the same user
72 that msmtpd runs as. Enable logging to syslog with --log=syslog.
73 Example for managing msmtpd with start-stop-daemon:
74 # start msmtpd
75 start-stop-daemon --start --pidfile /var/run/msmtpd.pid --make-pidfile
76 --chuid msmtpd --background --exec /usr/local/bin/msmtpd -- --command
77 '/usr/local/bin/msmtp -f %F --'
78 # stop msmtpd
79 start-stop-daemon --stop --pidfile /var/run/msmtpd.pid --remove-pid‐
80 file --quiet --signal TERM
81 Using msmtpd to handle outgoing mail for an SMTP-based mail client
82 Some mail clients cannot send outgoing mail with a program like msmtp
83 and instead insist on using an SMTP server. You can configure msmtpd to
84 be that SMTP server and hand your outgoing mail over to msmtp.
85 (Similarly, some mail clients cannot get incoming mail from a local
86 mailbox and insist on using a POP3 or IMAP server. You can configure
87 mpopd to be that POP3 server and serve incoming mail from a local mail‐
88 box. See the relevant section in the mpop manual.)
89 For this purpose, msmtpd should listen on an unprivileged port, e.g.
90 2500. Furthermore, msmtpd should require authentication because other‐
91 wise anyone connecting to it can send mail using your account, even if
92 it's just other users or processes on your local machine.
93 Let's use the user name msmtpd-user for this purpose. You have two op‐
94 tions to manage the password:
95 Store the password in your key ring, e.g. with secret-tool store
97 --label=msmtpd host localhost service smtp user msmtpd-user. In
98 this case, use the msmtpd option --auth=msmtpd-user.
99 Store the password in an encrypted file and use the passwordeval
101 mechanism. Example for gpg: msmtpd ... --auth=msmtpd-user,'gpg
102 -q -d ~/.msmtpd-password.gpg'
103 The complete command then is (using the keyring): msmtpd --port=2500
105 --auth=msmtpd-user --command='/path/to/your/msmtp -f %F --'
106 The mail client software must then be configured to use localhost at
107 port 2500 for outgoing mail via SMTP, and to use authentication with
108 user msmtpd-user and the password you chose. The mail client will prob‐
109 ably complain that the SMTP server does not support TLS, but in this
110 special case that is ok since all communication between your mail
111 client and msmtpd will stay on the local machine.
112 This setup also works with multiple mail accounts. Msmtp will pick the
113 correct one based on the envelope-from address given to it via -f %F.
114 You do not need multiple instances of msmtpd for this purpose, and
115 therefore you need only one SMTP server in your mail client configura‐
116 tion.
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119 msmtp(1)
120 2021-09 MSMTPD(1)