So if you’re looking for an easy way to relay outgoing emails based on sender address, give sender_dependent_default_transport_maps a try! To verify the above settings, I have sent an email from the terminal using [email protected] email address. As per the above configuration, the emails from should relay through SMTP server. As per the logs, the email was relayed through the correct SMTP server. For those who need to relay outgoing emails based on the sender address, the sender_dependent_default_transport_maps parameter in Postfix can come in handy. This parameter enables you to specify which transport a message should be routed through based on its sender address.

Postfix  Relay Outgoing Emails Based On Sender Address   TecAdmin - 75