Binding Outbound SMTP to a Source IP
Control the source address used by the Postfix SMTP client.
Production note: Back up configuration, run
postfix check, and stage changes before reloading.Core parameters
smtp_bind_address = 192.0.2.10
smtp_helo_name = mail.example.comMultiple IPs
For multiple source IPs, define dedicated transports in master.cf and route traffic using transport maps or sender-dependent transports.
Identity requirements
The selected IP should have matching PTR, forward DNS, HELO identity, SPF authorization, and aligned DKIM/DMARC for the message stream.
Test
postconf smtp_bind_address smtp_helo_name
swaks --server 127.0.0.1 --from [email protected] --to [email protected]