How to change postfix port from 25 to 587

Multiple possibilities

1. Antivirus software is blocking traffic going to port 25
2. Gateway/firewall is blocking
3. ISP is blocking

All the above are common causes.

If you are trying to use that server as your out going smtp, use port 587 or 465.

You may have to modify postfix configuration file your email server to enable the above ports.

In /etc/postfix/master.cf, look for following lines

#submission inet 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       -       -       -       -       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

Un-comment them (remove the # in the beginning of each line) and restart postfix.

The submission section enable port 587.

the smtps section enable port 465.

I also followed Flurdy's tutorial and had a similar problem: I could only send mail through port 25 (smtpd), but not through 587 (submission). I found out the problem to be exactly that, according to his instructions, port 25 was configured to run in chroot but 587 was not - it seems to be an error in the tutorial. Check out this part of flurdy's instructions:

By default only the normal smtp service is enabled, which is fine. But I prefer to enable submission (port 587), so that clients can use it, and I can restrict them to TLS only. Also enabled smtps service (port 465), for some compatebility with some older clients (outlook express etc).

Right below this text you can find this line, stating the daemon for the submission port will not use chroot:

submission inet n - n - - smtpd

I know this because my original /etc/postfix/master.cf file had comments showing this legend:

# ==========================================================================
# service type  private unpriv  chroot  wakeup  maxproc command + args
#               (yes)   (yes)   (yes)   (never) (100)
# ==========================================================================

Right below the option list for the submission port lies the following line, which configures smtps (port 465):

smtps inet n - - - - smtpd

From this you can see it is using the default (I guess the - sign means it will use the default, which is to use chroot).

Ok, then, when you look at the SASL authentication section, where it says:

Change how SASLAUTHD is run:

you can see the OPTIONS variable contains the following path:

# Switch this to be under postfix's spool
# And add -r so that the realm(domain) is part of the username
OPTIONS="-r -c -m /var/spool/postfix/var/run/saslauthd"

Again, with help from my originally commented /etc/default/saslauthd file, I noted this clear explanation:

# Other options (default: -c -m /var/run/saslauthd)
# Note: You MUST specify the -m option or saslauthd won't run!
#
# WARNING: DO NOT SPECIFY THE -d OPTION.
# The -d option will cause saslauthd to run in the foreground instead of as
# a daemon. This will PREVENT YOUR SYSTEM FROM BOOTING PROPERLY. If you wish
# to run saslauthd in debug mode, please run it by hand to be safe.
#
# See /usr/share/doc/sasl2-bin/README.Debian for Debian-specific information.
# See the saslauthd man page and the output of 'saslauthd -h' for general
# information about these options.
#
# Example for chroot Postfix users: "-c -m /var/spool/postfix/var/run/saslauthd"
# Example for non-chroot Postfix users: "-c -m /var/run/saslauthd"
#
# To know if your Postfix is running chroot, check /etc/postfix/master.cf.
# If it has the line "smtp inet n - y - - smtpd" or "smtp inet n - - - - smtpd"
# then your Postfix is running in a chroot.
# If it has the line "smtp inet n - n - - smtpd" then your Postfix is NOT
# running in a chroot.
OPTIONS="-r -c -m /var/spool/postfix/var/run/saslauthd"

Since my OPTIONS variable was clearly specifying the chroot case, I just changed my submission configuration at /etc/postfix/master.cf to also use chroot. After restarting the server - just to make sure all the services were properly restarted - it worked out like a charm, now I can send email either through port 25 or 587.

Hope it also helps you out! I also lost quite some time to see this...