Disable SMTP AUTH on Port 25

Yes, postfix is perfectly capable of this.

Take a look at the Postfix HOWTO:

http://postfix.state-of-mind.de/patrick.koetter/smtpauth/

and particularly:

http://postfix.state-of-mind.de/patrick.koetter/smtpauth/smtp_auth_mailclients.html

(those two pages are linked from the fairly extensive official Postfix docs page http://www.postfix.org/docs.html)

For my server, the configuration in master.cf looks like:

# ==========================================================================
# service type  private unpriv  chroot  wakeup  maxproc command + args
#               (yes)   (yes)   (yes)   (never) (100)
# ==========================================================================
smtp      inet  n       -       n       -       -       smtpd
submission inet n       -       n       -       -       smtpd
  -o smtpd_tls_security_level=encrypt
  -o smtpd_sasl_auth_enable=yes
  -o smtpd_client_restrictions=permit_sasl_authenticated,reject
  -o milter_macro_daemon_name=ORIGINATING
smtps     inet  n       -       n       -       -       smtpd
  -o smtpd_tls_wrappermode=yes
  -o smtpd_sasl_auth_enable=yes
  -o smtpd_client_restrictions=permit_sasl_authenticated,reject
  -o milter_macro_daemon_name=ORIGINATING

And main.cf has a line like:

smtpd_recipient_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination

In this case, authentication is only turned on for the submission (587) and SMTPS (465) ports.

It seems that the Postfix’s option smtpd_tls_auth_only = yes is exactly what you search. It allows to use SMTP AUTH only when TLS is activated, which is only relevant on port 25 for your configuration.

http://www.postfix.org/SASL_README.html#id396969
http://www.postfix.org/postconf.5.html#smtpd_tls_auth_only

Disable SMTP AUTH on Port 25

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