TLSPROXY(8) TLSPROXY(8)
NAME
tlsproxy - Postfix TLS proxy
SYNOPSIS
tlsproxy [generic Postfix daemon options]
DESCRIPTION
The tlsproxy(8) server implements a two-way TLS proxy. It is used by
the postscreen(8) server to talk SMTP-over-TLS with remote SMTP clients
that are not allowlisted (including clients whose allowlist status has
expired), and by the smtp(8) client to support TLS connection reuse,
but it should also work for non-SMTP protocols.
Although one tlsproxy(8) process can serve multiple sessions at the
same time, it is a good idea to allow the number of processes to
increase with load, so that the service remains responsive.
PROTOCOL EXAMPLE
The example below concerns postscreen(8). However, the tlsproxy(8)
server is agnostic of the application protocol, and the example is eas-
ily adapted to other applications.
After receiving a valid remote SMTP client STARTTLS command, the
postscreen(8) server sends the remote SMTP client endpoint string, the
requested role (server), and the requested timeout to tlsproxy(8).
postscreen(8) then receives a "TLS available" indication from
tlsproxy(8). If the TLS service is available, postscreen(8) sends the
remote SMTP client file descriptor to tlsproxy(8), and sends the plain-
text 220 greeting to the remote SMTP client. This triggers TLS negoti-
ations between the remote SMTP client and tlsproxy(8). Upon completion
of the TLS-level handshake, tlsproxy(8) translates between plaintext
from/to postscreen(8) and ciphertext to/from the remote SMTP client.
SECURITY
The tlsproxy(8) server is moderately security-sensitive. It talks to
untrusted clients on the network. The process can be run chrooted at
fixed low privilege.
DIAGNOSTICS
Problems and transactions are logged to syslogd(8) or postlogd(8).
CONFIGURATION PARAMETERS
Changes to main.cf are not picked up automatically, as tlsproxy(8) pro-
cesses may run for a long time depending on mail server load. Use the
command "postfix reload" to speed up a change.
The text below provides only a parameter summary. See postconf(5) for
more details including examples.
STARTTLS GLOBAL CONTROLS
The following settings are global and therefore cannot be overruled by
information specified in a tlsproxy(8) client request.
tls_append_default_CA (no)
Append the system-supplied default Certification Authority cer-
tificates to the ones specified with *_tls_CApath or
*_tls_CAfile.
tls_daemon_random_bytes (32)
The number of pseudo-random bytes that an smtp(8) or smtpd(8)
process requests from the tlsmgr(8) server in order to seed its
internal pseudo random number generator (PRNG).
tls_high_cipherlist (see 'postconf -d' output)
The OpenSSL cipherlist for "high" grade ciphers.
tls_medium_cipherlist (see 'postconf -d' output)
The OpenSSL cipherlist for "medium" or higher grade ciphers.
tls_low_cipherlist (see 'postconf -d' output)
The OpenSSL cipherlist for "low" or higher grade ciphers.
tls_export_cipherlist (see 'postconf -d' output)
The OpenSSL cipherlist for "export" or higher grade ciphers.
tls_null_cipherlist (eNULL:!aNULL)
The OpenSSL cipherlist for "NULL" grade ciphers that provide
authentication without encryption.
tls_eecdh_strong_curve (prime256v1)
The elliptic curve used by the Postfix SMTP server for sensibly
strong ephemeral ECDH key exchange.
tls_eecdh_ultra_curve (secp384r1)
The elliptic curve used by the Postfix SMTP server for maximally
strong ephemeral ECDH key exchange.
tls_disable_workarounds (see 'postconf -d' output)
List or bit-mask of OpenSSL bug work-arounds to disable.
tls_preempt_cipherlist (no)
With SSLv3 and later, use the Postfix SMTP server's cipher pref-
erence order instead of the remote client's cipher preference
order.
Available in Postfix version 2.9 and later:
tls_legacy_public_key_fingerprints (no)
A temporary migration aid for sites that use certificate pub-
lic-key fingerprints with Postfix 2.9.0..2.9.5, which use an
incorrect algorithm.
Available in Postfix version 2.11-3.1:
tls_dane_digest_agility (on)
Configure RFC7671 DANE TLSA digest algorithm agility.
tls_dane_trust_anchor_digest_enable (yes)
Enable support for RFC 6698 (DANE TLSA) DNS records that contain
digests of trust-anchors with certificate usage "2".
Available in Postfix version 2.11 and later:
tlsmgr_service_name (tlsmgr)
The name of the tlsmgr(8) service entry in master.cf.
Available in Postfix version 3.0 and later:
tls_session_ticket_cipher (Postfix >= 3.0: aes-256-cbc, Postfix < 3.0:
aes-128-cbc)
Algorithm used to encrypt RFC5077 TLS session tickets.
openssl_path (openssl)
The location of the OpenSSL command line program openssl(1).
Available in Postfix version 3.2 and later:
tls_eecdh_auto_curves (see 'postconf -d' output)
The prioritized list of elliptic curves supported by the Postfix
SMTP client and server.
Available in Postfix version 3.4 and later:
tls_server_sni_maps (empty)
Optional lookup tables that map names received from remote SMTP
clients via the TLS Server Name Indication (SNI) extension to
the appropriate keys and certificate chains.
Available in Postfix 3.5, 3.4.6, 3.3.5, 3.2.10, 3.1.13 and later:
tls_fast_shutdown_enable (yes)
A workaround for implementations that hang Postfix while shut-
ting down a TLS session, until Postfix times out.
STARTTLS SERVER CONTROLS
These settings are clones of Postfix SMTP server settings. They allow
tlsproxy(8) to load the same certificate and private key information as
the Postfix SMTP server, before dropping privileges, so that the key
files can be kept read-only for root. These settings can currently not
be overruled by information in a tlsproxy(8) client request, but that
limitation may be removed in a future version.
tlsproxy_tls_CAfile ($smtpd_tls_CAfile)
A file containing (PEM format) CA certificates of root CAs
trusted to sign either remote SMTP client certificates or inter-
mediate CA certificates.
tlsproxy_tls_CApath ($smtpd_tls_CApath)
A directory containing (PEM format) CA certificates of root CAs
trusted to sign either remote SMTP client certificates or inter-
mediate CA certificates.
tlsproxy_tls_always_issue_session_ids ($smtpd_tls_always_issue_ses-
sion_ids)
Force the Postfix tlsproxy(8) server to issue a TLS session id,
even when TLS session caching is turned off.
tlsproxy_tls_ask_ccert ($smtpd_tls_ask_ccert)
Ask a remote SMTP client for a client certificate.
tlsproxy_tls_ccert_verifydepth ($smtpd_tls_ccert_verifydepth)
The verification depth for remote SMTP client certificates.
tlsproxy_tls_cert_file ($smtpd_tls_cert_file)
File with the Postfix tlsproxy(8) server RSA certificate in PEM
format.
tlsproxy_tls_ciphers ($smtpd_tls_ciphers)
The minimum TLS cipher grade that the Postfix tlsproxy(8) server
will use with opportunistic TLS encryption.
tlsproxy_tls_dcert_file ($smtpd_tls_dcert_file)
File with the Postfix tlsproxy(8) server DSA certificate in PEM
format.
tlsproxy_tls_dh1024_param_file ($smtpd_tls_dh1024_param_file)
File with DH parameters that the Postfix tlsproxy(8) server
should use with non-export EDH ciphers.
tlsproxy_tls_dh512_param_file ($smtpd_tls_dh512_param_file)
File with DH parameters that the Postfix tlsproxy(8) server
should use with export-grade EDH ciphers.
tlsproxy_tls_dkey_file ($smtpd_tls_dkey_file)
File with the Postfix tlsproxy(8) server DSA private key in PEM
format.
tlsproxy_tls_eccert_file ($smtpd_tls_eccert_file)
File with the Postfix tlsproxy(8) server ECDSA certificate in
PEM format.
tlsproxy_tls_eckey_file ($smtpd_tls_eckey_file)
File with the Postfix tlsproxy(8) server ECDSA private key in
PEM format.
tlsproxy_tls_eecdh_grade ($smtpd_tls_eecdh_grade)
The Postfix tlsproxy(8) server security grade for ephemeral
elliptic-curve Diffie-Hellman (EECDH) key exchange.
tlsproxy_tls_exclude_ciphers ($smtpd_tls_exclude_ciphers)
List of ciphers or cipher types to exclude from the tlsproxy(8)
server cipher list at all TLS security levels.
tlsproxy_tls_fingerprint_digest ($smtpd_tls_fingerprint_digest)
The message digest algorithm to construct remote SMTP
client-certificate fingerprints.
tlsproxy_tls_key_file ($smtpd_tls_key_file)
File with the Postfix tlsproxy(8) server RSA private key in PEM
format.
tlsproxy_tls_loglevel ($smtpd_tls_loglevel)
Enable additional Postfix tlsproxy(8) server logging of TLS
activity.
tlsproxy_tls_mandatory_ciphers ($smtpd_tls_mandatory_ciphers)
The minimum TLS cipher grade that the Postfix tlsproxy(8) server
will use with mandatory TLS encryption.
tlsproxy_tls_mandatory_exclude_ciphers ($smtpd_tls_manda-
tory_exclude_ciphers)
Additional list of ciphers or cipher types to exclude from the
tlsproxy(8) server cipher list at mandatory TLS security levels.
tlsproxy_tls_mandatory_protocols ($smtpd_tls_mandatory_protocols)
The SSL/TLS protocols accepted by the Postfix tlsproxy(8) server
with mandatory TLS encryption.
tlsproxy_tls_protocols ($smtpd_tls_protocols)
List of TLS protocols that the Postfix tlsproxy(8) server will
exclude or include with opportunistic TLS encryption.
tlsproxy_tls_req_ccert ($smtpd_tls_req_ccert)
With mandatory TLS encryption, require a trusted remote SMTP
client certificate in order to allow TLS connections to proceed.
tlsproxy_tls_security_level ($smtpd_tls_security_level)
The SMTP TLS security level for the Postfix tlsproxy(8) server;
when a non-empty value is specified, this overrides the obsolete
parameters smtpd_use_tls and smtpd_enforce_tls.
tlsproxy_tls_chain_files ($smtpd_tls_chain_files)
Files with the Postfix tlsproxy(8) server keys and certificate
chains in PEM format.
STARTTLS CLIENT CONTROLS
These settings are clones of Postfix SMTP client settings. They allow
tlsproxy(8) to load the same certificate and private key information as
the Postfix SMTP client, before dropping privileges, so that the key
files can be kept read-only for root. Some settings may be overruled by
information in a tlsproxy(8) client request.
Available in Postfix version 3.4 and later:
tlsproxy_client_CAfile ($smtp_tls_CAfile)
A file containing CA certificates of root CAs trusted to sign
either remote TLS server certificates or intermediate CA cer-
tificates.
tlsproxy_client_CApath ($smtp_tls_CApath)
Directory with PEM format Certification Authority certificates
that the Postfix tlsproxy(8) client uses to verify a remote TLS
server certificate.
tlsproxy_client_chain_files ($smtp_tls_chain_files)
Files with the Postfix tlsproxy(8) client keys and certificate
chains in PEM format.
tlsproxy_client_cert_file ($smtp_tls_cert_file)
File with the Postfix tlsproxy(8) client RSA certificate in PEM
format.
tlsproxy_client_key_file ($smtp_tls_key_file)
File with the Postfix tlsproxy(8) client RSA private key in PEM
format.
tlsproxy_client_dcert_file ($smtp_tls_dcert_file)
File with the Postfix tlsproxy(8) client DSA certificate in PEM
format.
tlsproxy_client_dkey_file ($smtp_tls_dkey_file)
File with the Postfix tlsproxy(8) client DSA private key in PEM
format.
tlsproxy_client_eccert_file ($smtp_tls_eccert_file)
File with the Postfix tlsproxy(8) client ECDSA certificate in
PEM format.
tlsproxy_client_eckey_file ($smtp_tls_eckey_file)
File with the Postfix tlsproxy(8) client ECDSA private key in
PEM format.
tlsproxy_client_fingerprint_digest ($smtp_tls_fingerprint_digest)
The message digest algorithm used to construct remote TLS server
certificate fingerprints.
tlsproxy_client_loglevel ($smtp_tls_loglevel)
Enable additional Postfix tlsproxy(8) client logging of TLS
activity.
tlsproxy_client_loglevel_parameter (smtp_tls_loglevel)
The name of the parameter that provides the
tlsproxy_client_loglevel value.
tlsproxy_client_scert_verifydepth ($smtp_tls_scert_verifydepth)
The verification depth for remote TLS server certificates.
tlsproxy_client_security_level ($smtp_tls_security_level)
The default TLS security level for the Postfix tlsproxy(8)
client.
tlsproxy_client_policy_maps ($smtp_tls_policy_maps)
Optional lookup tables with the Postfix tlsproxy(8) client TLS
security policy by next-hop destination.
tlsproxy_client_use_tls ($smtp_use_tls)
Opportunistic mode: use TLS when a remote server announces TLS
support.
tlsproxy_client_enforce_tls ($smtp_enforce_tls)
Enforcement mode: require that SMTP servers use TLS encryption.
tlsproxy_client_per_site ($smtp_tls_per_site)
Optional lookup tables with the Postfix tlsproxy(8) client TLS
usage policy by next-hop destination and by remote TLS server
hostname.
OBSOLETE STARTTLS SUPPORT CONTROLS
These parameters are supported for compatibility with smtpd(8) legacy
parameters.
tlsproxy_use_tls ($smtpd_use_tls)
Opportunistic TLS: announce STARTTLS support to remote SMTP
clients, but do not require that clients use TLS encryption.
tlsproxy_enforce_tls ($smtpd_enforce_tls)
Mandatory TLS: announce STARTTLS support to remote SMTP clients,
and require that clients use TLS encryption.
RESOURCE CONTROLS
tlsproxy_watchdog_timeout (10s)
How much time a tlsproxy(8) process may take to process local or
remote I/O before it is terminated by a built-in watchdog timer.
MISCELLANEOUS CONTROLS
config_directory (see 'postconf -d' output)
The default location of the Postfix main.cf and master.cf con-
figuration files.
process_id (read-only)
The process ID of a Postfix command or daemon process.
process_name (read-only)
The process name of a Postfix command or daemon process.
syslog_facility (mail)
The syslog facility of Postfix logging.
syslog_name (see 'postconf -d' output)
A prefix that is prepended to the process name in syslog
records, so that, for example, "smtpd" becomes "prefix/smtpd".
Available in Postfix 3.3 and later:
service_name (read-only)
The master.cf service name of a Postfix daemon process.
SEE ALSO
postscreen(8), Postfix zombie blocker
smtpd(8), Postfix SMTP server
postconf(5), configuration parameters
postlogd(8), Postfix logging
syslogd(8), system logging
LICENSE
The Secure Mailer license must be distributed with this software.
HISTORY
This service was introduced with Postfix version 2.8.
AUTHOR(S)
Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA
Wietse Venema
Google, Inc.
111 8th Avenue
New York, NY 10011, USA
TLSPROXY(8)