I'm using postfix as a mail relay in a very simple setup, mostly with aliases, forwarding mails to GMail.

My main goal with this is to minimize the need for mailboxes on my server.

Let's assume I have the following alias

bob@mydomain.tld -> bob@gmail.com

I would like to redirect/forward all incoming mail for bob@mydomain.tld to the GMail account bob@mydomain.tld. That's the easy part.

Now for all outgoing mail sent by bob@mydomain.tld GMail offers me the feature to send mails in behalf of a different account in the settings.

However, in order for this to work, GMail needs to be able to login via SMTP for bob@mydomain.tld, which is just an alias.

Is there a way to forward incoming mails with an alias by still being able to send mails via SMTP/SASL?

  • In GMail I added an account for bob@mydomain.tld under settings > accounts and import > send mail as, which only works if bob@mydomain.tld is an actual mailbox. The Google part is not a problem, it's simply adding an SMTP server with credentials. The postfix part is the problem. I don't want a mailbox. I just want to have an alias for incoming and SMTP/SASL auth for outgoing – mefiX Mar 14 '19 at 9:47

Meanwhile I managed to "solve" it - at least for my own personal needs.

I added the mailbox/user/login bob@mydomain.tld in order to enable the SASL authentication for that particular user.

Then, instead of adding an alias, I added the following recipient map

bob@mydomain.tld -> bob@gmail.com

Which means I can

  1. Receive all mail with the GMail account bob@gmail.com; and
  2. SMTP login and SASL auth. as bob@mydomain.tld in order to send mail; and
  3. Do no. (2) from the GMail account

So the mailbox is there, but it won't take up any actual space, because all mail will be redirected to GMail.

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