I currently have Postfix relaying multiple hosted customer solutions which all works as expected. There are no local accounts and it is used solely as a relay server.

In the config I have the following:

mydomain = hostdomain.com
myorigin = $mydomain

In email headers sent from the relay the following lines are seen:

Received: from mailrelay.hostdomain.com ([])
Received: from sendername (unknown [])
    by mailrelay.hostdomain.com (Postfix) with ESMTP id 6119FA0441
    for <end.user@gmail.com>; Wed, 16 Apr 2014 01:00:00 +0100 (BST)

We have multiple customers who wish to relay presenting themselves rather than as the server name. Examples being:

Customer Domain - customer1a.com
Desired Headers:

Received: from mailrelay.customer1a.com ([])
Received: from sendername (unknown [])
    by mailrelay.customer1a.com (Postfix) with ESMTP id 6119FA0441
    for <end.user@gmail.com>; Wed, 16 Apr 2014 01:00:00 +0100 (BST)

Customer Domain - customer2b.com
Desired Headers:

Received: from mailrelay.customer2b.com ([])
Received: from sendername (unknown [])
    by mailrelay.customer2b.com (Postfix) with ESMTP id 6119FA0441
    for <end.user@gmail.com>; Wed, 16 Apr 2014 01:00:00 +0100 (BST)

Is this possible to achieve? The documentation I have read includes virtual aliases but I can't see a way listed to achieve the above?


You could run multiple postfix instances, one for each customer. This would require either separate IPs or separate ports, separate queue directories, etc.

Otherwise, no - this is not how it works. And it's not as if their recipients will be looking at the headers anyway, most people won't even know how to find them, so it's not an issue of presentation.

It's possible that the real problem they're having is that the mail gets marked as spam because a lot of mail is coming from your servers and they don't match the sending domains. If so, they might publish SPF/DKIM records allowing your server to send mail on their behalf, to reduce the likelihood of this.

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