/@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/ restart postfix

# service postfix restart

to set for server-wide for all clients
You want smtp_bind_address=66.66.66.67 and inet_interfaces=all
or inet_interfaces=eth(whatever) that 66.66.66.67 is on.
and RESTART postfix