I have a Postfix server and using it with Outlook (POP/SMTP).

I have different sender addresses for an account. Now I want to configure a relay for a specific sender address. For example I have postfix for my main domain domain1.com. Now I have a sender address that is domain2.com.

For that sender address I want that postfix to relay mail to a second SMTP server. I think that should be possible without problems.

But the problem is that I have to create a SSH tunnel to the second server to connect to the SMTP server. But I cant use a persistent SSH connection so I want to know if it is possible that postfix executes some script before relaying the mail to the second SMTP server.

I already found some information for executing a script when incomming emails but I only want to establish the SSH tunnel before postfix relays the mail to the second SMTP server.