Recently there have been requests for sending mail with source IP addresses that depend on the envelope sender, it’s very usefull to protect IP-based domain reputations of different customers.

New Feature in postfix postfix-2.7-20091209 is sender_dependent_default_transport_maps

sender_dependent_default_transport_maps (default: empty)

    A sender-dependent override for the global default_transport parameter setting.
    The tables are searched by the envelope sender address and @domain.
    A lookup result of DUNNO terminates the search without overriding the global default_transport parameter setting.
    This information is overruled with the transport(5) table.

    Note: this overrides default_transport, not transport_maps, and therefore the expected syntax is that of default_transport.
          This feature does not support the transport_maps syntax for null transport, null nexthop, or null email addresses.

    For safety reasons, this feature does not allow $number substitutions in regular expression maps.

    This feature is available in Postfix 2.7 and later.

Create file called sdd_transport_maps.regexp:

/@customer1-dom\.tld$/		customer1:
/@customer2-dom\.tld$/		customer2:
/@customer3-dom\.tld$/		customer3:
..... next .....

In master.cf create special transport called customer1, customer2, customer3….and so on

customer1  unix -       -       n       -       -       smtp
   -o smtp_bind_address=1.1.1.1
   -o smtp_helo_name=customer1-dom.tld
   -o syslog_name=postfix-customer1

customer2  unix -       -       n       -       -       smtp
   -o smtp_bind_address=1.1.1.2
   -o smtp_helo_name=customer2-dom.tld
   -o syslog_name=postfix-customer2

customer3  unix -       -       n       -       -       smtp
   -o smtp_bind_address=1.1.1.3
   -o smtp_helo_name=customer3-dom.tld
   -o syslog_name=postfix-customer3

..... next .....

In main.cf add sender_dependent_default_transport_maps line:

sender_dependent_default_transport_maps = regexp:/etc/postfix/sdd_transport_maps.regexp

Don’t forget to create ip aliasing for each ip address in smtp_bind_address

reload postfix

# postfix reload
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