Send out email from specified IP address

If you have multiple IP addresses available on your iRedMail server, and would like to send from different IP Addresses for different domains, follow the steps below.

Requirement

This can only be set up on Postfix version >=2.7.x, because the parameter we need sender_dependent_default_transport_maps is available in Postfix-2.7 and later releases.

To check your Postfix version run:

# postconf mail_version

Which would return something like: mail_version = 2.10.3

Steps

Add Postfix setting sender_dependent_default_transport_maps to the end of /etc/postfix/main.cf like below:

sender_dependent_default_transport_maps = pcre:/etc/postfix/sdd_transport.pcre

Add file /etc/postfix/sdd_transport.pcre with below content. NOTE: we use domain example.com for example, it will use transport sample-smtp - see examples.

/@example\.com$/   sample-smtp:

Create new outgoing SMTP transports in /etc/postfix/master.cf like below. Note: you must replace our sample IP address 172.16.244.159 with your IP address. If you want to use IPv6 address, please use smtp_bind_address6 instead of smtp_bind_address below.

sample-smtp     unix -       -       n       -       -       smtp
    -o smtp_bind_address=172.16.244.159
#    -o smtp_helo_name=example.com
#    -o syslog_name=postfix-example-com

Option smtp_helo_name and syslog_name are optional.

After this restart the Postfix service to apply your changes:

# /etc/init.d/postfix restart

Note: any unmatched domains will continue using the server's primary IP address just as before.