1TLSPROXY(8) System Manager's Manual TLSPROXY(8)
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6 tlsproxy - Postfix TLS proxy
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9 tlsproxy [generic Postfix daemon options]
10
12 The tlsproxy(8) server implements a two-way TLS proxy. It is used by
13 the postscreen(8) server to talk SMTP-over-TLS with remote SMTP clients
14 that are not allowlisted (including clients whose allowlist status has
15 expired), and by the smtp(8) client to support TLS connection reuse,
16 but it should also work for non-SMTP protocols.
17 Although one tlsproxy(8) process can serve multiple sessions at the
19 same time, it is a good idea to allow the number of processes to in‐
20 crease with load, so that the service remains responsive.
21
23 The example below concerns postscreen(8). However, the tlsproxy(8)
24 server is agnostic of the application protocol, and the example is eas‐
25 ily adapted to other applications.
26 After receiving a valid remote SMTP client STARTTLS command, the
28 postscreen(8) server sends the remote SMTP client endpoint string, the
29 requested role (server), and the requested timeout to tlsproxy(8).
30 postscreen(8) then receives a "TLS available" indication from tl‐
31 sproxy(8). If the TLS service is available, postscreen(8) sends the
32 remote SMTP client file descriptor to tlsproxy(8), and sends the plain‐
33 text 220 greeting to the remote SMTP client. This triggers TLS negoti‐
34 ations between the remote SMTP client and tlsproxy(8). Upon completion
35 of the TLS-level handshake, tlsproxy(8) translates between plaintext
36 from/to postscreen(8) and ciphertext to/from the remote SMTP client.
37
39 The tlsproxy(8) server is moderately security-sensitive. It talks to
40 untrusted clients on the network. The process can be run chrooted at
41 fixed low privilege.
42
44 Problems and transactions are logged to syslogd(8) or postlogd(8).
45
47 Changes to main.cf are not picked up automatically, as tlsproxy(8) pro‐
48 cesses may run for a long time depending on mail server load. Use the
49 command "postfix reload" to speed up a change.
50 The text below provides only a parameter summary. See postconf(5) for
52 more details including examples.
53
55 The following settings are global and therefore cannot be overruled by
56 information specified in a tlsproxy(8) client request.
57 tls_append_default_CA (no)
59 Append the system-supplied default Certification Authority cer‐
60 tificates to the ones specified with *_tls_CApath or
61 *_tls_CAfile.
62 tls_daemon_random_bytes (32)
64 The number of pseudo-random bytes that an smtp(8) or smtpd(8)
65 process requests from the tlsmgr(8) server in order to seed its
66 internal pseudo random number generator (PRNG).
67 tls_high_cipherlist (see 'postconf -d' output)
69 The OpenSSL cipherlist for "high" grade ciphers.
70 tls_medium_cipherlist (see 'postconf -d' output)
72 The OpenSSL cipherlist for "medium" or higher grade ciphers.
73 tls_null_cipherlist (eNULL:!aNULL)
75 The OpenSSL cipherlist for "NULL" grade ciphers that provide au‐
76 thentication without encryption.
77 tls_eecdh_strong_curve (prime256v1)
79 The elliptic curve used by the Postfix SMTP server for sensibly
80 strong ephemeral ECDH key exchange.
81 tls_eecdh_ultra_curve (secp384r1)
83 The elliptic curve used by the Postfix SMTP server for maximally
84 strong ephemeral ECDH key exchange.
85 tls_disable_workarounds (see 'postconf -d' output)
87 List or bit-mask of OpenSSL bug work-arounds to disable.
88 tls_preempt_cipherlist (no)
90 With SSLv3 and later, use the Postfix SMTP server's cipher pref‐
91 erence order instead of the remote client's cipher preference
92 order.
93 Available in Postfix version 2.8..3.7:
95 tls_low_cipherlist (see 'postconf -d' output)
97 The OpenSSL cipherlist for "low" or higher grade ciphers.
98 tls_export_cipherlist (see 'postconf -d' output)
100 The OpenSSL cipherlist for "export" or higher grade ciphers.
101 Available in Postfix version 2.9 and later:
103 tls_legacy_public_key_fingerprints (no)
105 A temporary migration aid for sites that use certificate pub‐
106 lic-key fingerprints with Postfix 2.9.0..2.9.5, which use an in‐
107 correct algorithm.
108 Available in Postfix version 2.11-3.1:
110 tls_dane_digest_agility (on)
112 Configure RFC7671 DANE TLSA digest algorithm agility.
113 tls_dane_trust_anchor_digest_enable (yes)
115 Enable support for RFC 6698 (DANE TLSA) DNS records that contain
116 digests of trust-anchors with certificate usage "2".
117 Available in Postfix version 2.11 and later:
119 tlsmgr_service_name (tlsmgr)
121 The name of the tlsmgr(8) service entry in master.cf.
122 Available in Postfix version 3.0 and later:
124 tls_session_ticket_cipher (Postfix >= 3.0: aes-256-cbc, Postfix < 3.0:
126 aes-128-cbc)
127 Algorithm used to encrypt RFC5077 TLS session tickets.
128 openssl_path (openssl)
130 The location of the OpenSSL command line program openssl(1).
131 Available in Postfix version 3.2 and later:
133 tls_eecdh_auto_curves (see 'postconf -d' output)
135 The prioritized list of elliptic curves supported by the Postfix
136 SMTP client and server.
137 Available in Postfix version 3.4 and later:
139 tls_server_sni_maps (empty)
141 Optional lookup tables that map names received from remote SMTP
142 clients via the TLS Server Name Indication (SNI) extension to
143 the appropriate keys and certificate chains.
144 Available in Postfix 3.5, 3.4.6, 3.3.5, 3.2.10, 3.1.13 and later:
146 tls_fast_shutdown_enable (yes)
148 A workaround for implementations that hang Postfix while shut‐
149 ting down a TLS session, until Postfix times out.
150 Available in Postfix version 3.8 and later:
152 tls_ffdhe_auto_groups (see 'postconf -d' output)
154 The prioritized list of finite-field Diffie-Hellman ephemeral
155 (FFDHE) key exchange groups supported by the Postfix SMTP client
156 and server.
157 Available in Postfix 3.9, 3.8.1, 3.7.6, 3.6.10, 3.5.20 and later:
159 tls_config_file (default)
161 Optional configuration file with baseline OpenSSL settings.
162 tls_config_name (empty)
164 The application name passed by Postfix to OpenSSL library ini‐
165 tialization functions.
166
168 These settings are clones of Postfix SMTP server settings. They allow
169 tlsproxy(8) to load the same certificate and private key information as
170 the Postfix SMTP server, before dropping privileges, so that the key
171 files can be kept read-only for root. These settings can currently not
172 be overruled by information in a tlsproxy(8) client request, but that
173 limitation may be removed in a future version.
174 tlsproxy_tls_CAfile ($smtpd_tls_CAfile)
176 A file containing (PEM format) CA certificates of root CAs
177 trusted to sign either remote SMTP client certificates or inter‐
178 mediate CA certificates.
179 tlsproxy_tls_CApath ($smtpd_tls_CApath)
181 A directory containing (PEM format) CA certificates of root CAs
182 trusted to sign either remote SMTP client certificates or inter‐
183 mediate CA certificates.
184 tlsproxy_tls_always_issue_session_ids ($smtpd_tls_always_issue_ses‐
186 sion_ids)
187 Force the Postfix tlsproxy(8) server to issue a TLS session id,
188 even when TLS session caching is turned off.
189 tlsproxy_tls_ask_ccert ($smtpd_tls_ask_ccert)
191 Ask a remote SMTP client for a client certificate.
192 tlsproxy_tls_ccert_verifydepth ($smtpd_tls_ccert_verifydepth)
194 The verification depth for remote SMTP client certificates.
195 tlsproxy_tls_cert_file ($smtpd_tls_cert_file)
197 File with the Postfix tlsproxy(8) server RSA certificate in PEM
198 format.
199 tlsproxy_tls_ciphers ($smtpd_tls_ciphers)
201 The minimum TLS cipher grade that the Postfix tlsproxy(8) server
202 will use with opportunistic TLS encryption.
203 tlsproxy_tls_dcert_file ($smtpd_tls_dcert_file)
205 File with the Postfix tlsproxy(8) server DSA certificate in PEM
206 format.
207 tlsproxy_tls_dh1024_param_file ($smtpd_tls_dh1024_param_file)
209 File with DH parameters that the Postfix tlsproxy(8) server
210 should use with non-export EDH ciphers.
211 tlsproxy_tls_dh512_param_file ($smtpd_tls_dh512_param_file)
213 File with DH parameters that the Postfix tlsproxy(8) server
214 should use with export-grade EDH ciphers.
215 tlsproxy_tls_dkey_file ($smtpd_tls_dkey_file)
217 File with the Postfix tlsproxy(8) server DSA private key in PEM
218 format.
219 tlsproxy_tls_eccert_file ($smtpd_tls_eccert_file)
221 File with the Postfix tlsproxy(8) server ECDSA certificate in
222 PEM format.
223 tlsproxy_tls_eckey_file ($smtpd_tls_eckey_file)
225 File with the Postfix tlsproxy(8) server ECDSA private key in
226 PEM format.
227 tlsproxy_tls_eecdh_grade ($smtpd_tls_eecdh_grade)
229 The Postfix tlsproxy(8) server security grade for ephemeral el‐
230 liptic-curve Diffie-Hellman (EECDH) key exchange.
231 tlsproxy_tls_exclude_ciphers ($smtpd_tls_exclude_ciphers)
233 List of ciphers or cipher types to exclude from the tlsproxy(8)
234 server cipher list at all TLS security levels.
235 tlsproxy_tls_fingerprint_digest ($smtpd_tls_fingerprint_digest)
237 The message digest algorithm to construct remote SMTP
238 client-certificate fingerprints.
239 tlsproxy_tls_key_file ($smtpd_tls_key_file)
241 File with the Postfix tlsproxy(8) server RSA private key in PEM
242 format.
243 tlsproxy_tls_loglevel ($smtpd_tls_loglevel)
245 Enable additional Postfix tlsproxy(8) server logging of TLS ac‐
246 tivity.
247 tlsproxy_tls_mandatory_ciphers ($smtpd_tls_mandatory_ciphers)
249 The minimum TLS cipher grade that the Postfix tlsproxy(8) server
250 will use with mandatory TLS encryption.
251 tlsproxy_tls_mandatory_exclude_ciphers ($smtpd_tls_mandatory_ex‐
253 clude_ciphers)
254 Additional list of ciphers or cipher types to exclude from the
255 tlsproxy(8) server cipher list at mandatory TLS security levels.
256 tlsproxy_tls_mandatory_protocols ($smtpd_tls_mandatory_protocols)
258 The SSL/TLS protocols accepted by the Postfix tlsproxy(8) server
259 with mandatory TLS encryption.
260 tlsproxy_tls_protocols ($smtpd_tls_protocols)
262 List of TLS protocols that the Postfix tlsproxy(8) server will
263 exclude or include with opportunistic TLS encryption.
264 tlsproxy_tls_req_ccert ($smtpd_tls_req_ccert)
266 With mandatory TLS encryption, require a trusted remote SMTP
267 client certificate in order to allow TLS connections to proceed.
268 tlsproxy_tls_security_level ($smtpd_tls_security_level)
270 The SMTP TLS security level for the Postfix tlsproxy(8) server;
271 when a non-empty value is specified, this overrides the obsolete
272 parameters smtpd_use_tls and smtpd_enforce_tls.
273 tlsproxy_tls_chain_files ($smtpd_tls_chain_files)
275 Files with the Postfix tlsproxy(8) server keys and certificate
276 chains in PEM format.
277
279 These settings are clones of Postfix SMTP client settings. They allow
280 tlsproxy(8) to load the same certificate and private key information as
281 the Postfix SMTP client, before dropping privileges, so that the key
282 files can be kept read-only for root. Some settings may be overruled by
283 information in a tlsproxy(8) client request.
284 Available in Postfix version 3.4 and later:
286 tlsproxy_client_CAfile ($smtp_tls_CAfile)
288 A file containing CA certificates of root CAs trusted to sign
289 either remote TLS server certificates or intermediate CA cer‐
290 tificates.
291 tlsproxy_client_CApath ($smtp_tls_CApath)
293 Directory with PEM format Certification Authority certificates
294 that the Postfix tlsproxy(8) client uses to verify a remote TLS
295 server certificate.
296 tlsproxy_client_chain_files ($smtp_tls_chain_files)
298 Files with the Postfix tlsproxy(8) client keys and certificate
299 chains in PEM format.
300 tlsproxy_client_cert_file ($smtp_tls_cert_file)
302 File with the Postfix tlsproxy(8) client RSA certificate in PEM
303 format.
304 tlsproxy_client_key_file ($smtp_tls_key_file)
306 File with the Postfix tlsproxy(8) client RSA private key in PEM
307 format.
308 tlsproxy_client_dcert_file ($smtp_tls_dcert_file)
310 File with the Postfix tlsproxy(8) client DSA certificate in PEM
311 format.
312 tlsproxy_client_dkey_file ($smtp_tls_dkey_file)
314 File with the Postfix tlsproxy(8) client DSA private key in PEM
315 format.
316 tlsproxy_client_eccert_file ($smtp_tls_eccert_file)
318 File with the Postfix tlsproxy(8) client ECDSA certificate in
319 PEM format.
320 tlsproxy_client_eckey_file ($smtp_tls_eckey_file)
322 File with the Postfix tlsproxy(8) client ECDSA private key in
323 PEM format.
324 tlsproxy_client_fingerprint_digest ($smtp_tls_fingerprint_digest)
326 The message digest algorithm used to construct remote TLS server
327 certificate fingerprints.
328 tlsproxy_client_loglevel ($smtp_tls_loglevel)
330 Enable additional Postfix tlsproxy(8) client logging of TLS ac‐
331 tivity.
332 tlsproxy_client_loglevel_parameter (smtp_tls_loglevel)
334 The name of the parameter that provides the tl‐
335 sproxy_client_loglevel value.
336 tlsproxy_client_scert_verifydepth ($smtp_tls_scert_verifydepth)
338 The verification depth for remote TLS server certificates.
339 tlsproxy_client_use_tls ($smtp_use_tls)
341 Opportunistic mode: use TLS when a remote server announces TLS
342 support.
343 tlsproxy_client_enforce_tls ($smtp_enforce_tls)
345 Enforcement mode: require that SMTP servers use TLS encryption.
346 tlsproxy_client_per_site ($smtp_tls_per_site)
348 Optional lookup tables with the Postfix tlsproxy(8) client TLS
349 usage policy by next-hop destination and by remote TLS server
350 hostname.
351 Available in Postfix version 3.4-3.6:
353 tlsproxy_client_level ($smtp_tls_security_level)
355 The default TLS security level for the Postfix tlsproxy(8)
356 client.
357 tlsproxy_client_policy ($smtp_tls_policy_maps)
359 Optional lookup tables with the Postfix tlsproxy(8) client TLS
360 security policy by next-hop destination.
361 Available in Postfix version 3.7 and later:
363 tlsproxy_client_security_level ($smtp_tls_security_level)
365 The default TLS security level for the Postfix tlsproxy(8)
366 client.
367 tlsproxy_client_policy_maps ($smtp_tls_policy_maps)
369 Optional lookup tables with the Postfix tlsproxy(8) client TLS
370 security policy by next-hop destination.
371
373 These parameters are supported for compatibility with smtpd(8) legacy
374 parameters.
375 tlsproxy_use_tls ($smtpd_use_tls)
377 Opportunistic TLS: announce STARTTLS support to remote SMTP
378 clients, but do not require that clients use TLS encryption.
379 tlsproxy_enforce_tls ($smtpd_enforce_tls)
381 Mandatory TLS: announce STARTTLS support to remote SMTP clients,
382 and require that clients use TLS encryption.
383 tlsproxy_client_use_tls ($smtp_use_tls)
385 Opportunistic mode: use TLS when a remote server announces TLS
386 support.
387 tlsproxy_client_enforce_tls ($smtp_enforce_tls)
389 Enforcement mode: require that SMTP servers use TLS encryption.
390
392 tlsproxy_watchdog_timeout (10s)
393 How much time a tlsproxy(8) process may take to process local or
394 remote I/O before it is terminated by a built-in watchdog timer.
395
397 config_directory (see 'postconf -d' output)
398 The default location of the Postfix main.cf and master.cf con‐
399 figuration files.
400 process_id (read-only)
402 The process ID of a Postfix command or daemon process.
403 process_name (read-only)
405 The process name of a Postfix command or daemon process.
406 syslog_facility (mail)
408 The syslog facility of Postfix logging.
409 syslog_name (see 'postconf -d' output)
411 A prefix that is prepended to the process name in syslog
412 records, so that, for example, "smtpd" becomes "prefix/smtpd".
413 Available in Postfix 3.3 and later:
415 service_name (read-only)
417 The master.cf service name of a Postfix daemon process.
418
420 postscreen(8), Postfix zombie blocker
421 smtpd(8), Postfix SMTP server
422 postconf(5), configuration parameters
423 postlogd(8), Postfix logging
424 syslogd(8), system logging
425
427 The Secure Mailer license must be distributed with this software.
428
430 This service was introduced with Postfix version 2.8.
431
433 Wietse Venema
434 IBM T.J. Watson Research
435 P.O. Box 704
436 Yorktown Heights, NY 10598, USA
437 Wietse Venema
439 Google, Inc.
440 111 8th Avenue
441 New York, NY 10011, USA
442 TLSPROXY(8)