This is a followup to a serverfault post I made a while ago:

How do I target a different mail server depending on domain with exim?

(More context here too: http://forum.slicehost.com/comments.php?DiscussionID=3806 )

I have a slice/VPS at Slicehost. I basically decided to scrap exim (i.e., purge it), and start anew with my email infrastructure. In case you didn't read any of the above threads, basically my goal was to have a send only mail infrastructure that relays all outgoing email to Google Apps. I also wanted to where email from domain1 (a Wordpress installation) would show it coming from domain1.com and email from domain2 (a normal website) would show it coming from domain2.com.

So I decided to give PostFix a try. I literally followed the surprisingly simple instructions here:


And voila, all seems to be working as I expected. My email tests show email coming from the proper locations (either domain1 or domain2 depending on where the emails were sent from).

But this all seemed too simple to me. So simple, in fact, that I feel that something is amiss.

When I installed PostFix according to the instructions in the post above and it worked, I was surprised that I didn't have to specify an SMTP server, a port number, any authentication credentials, etc. My slice is set up such that I have MX records for Google Apps (e.g., ASPMX.L.GOOGLE.COM.) in my DNS settings, but I am not sure if that is why it is working.

My email infrastructure knowledge is admittedly limited, but with this am I suspect to:

  1. Spammers using my email infrastructure?
  2. My emails going to people as spam?
  3. Something else sinister?

I have actually stopped running PostFix until I understand this better.


  • Side note - Exim has been nothing but excellent to me, and while I hear good things about Postfix also, it's a shame you couldn't get Exim to solve your problem. – crb Jun 25 '09 at 21:04

Generally speaking, I find postfix to have pretty good settings out of the box. If you're concerned about other people abusing it, run it through abuse.net's relay testing, which should answer #1.

2 - that depends on how others have their spam filters configured, but you should be fine. You could test this by signing up for & sending to a few free accounts (Hotmail, Gmail, and Yahoo will cover most of the mainstream configurations, including DKIM, SPF, Postini, etc)

3 - You haven't missed anything major that I can think of off the top of my head... I'd say just test the heck out of it, watch your logs for the first week, and you should be good to go.

  • Thank you! Well, I am finding through other posts I have made with this question that, unbeknownst to me, my mail is no longer being relayed through Google Apps at all. Postfix is the default sender now. It just looks like when I test that the email was sent from Google Apps because the From: address is an address that I have set up in Google Apps. – Joel Marcey Jun 25 '09 at 21:39
  • Also, I have to adjust my thinking to this new way of handling email. When I was using exim4, I was quite certain I was relaying through Gmail/Google Apps because I had settings in a passwd.client file and all the email looked like it was coming from that account. For example, when I went through the Postfix setup "wizard" it asked me for my System Mail Name, and I basically just put what I named my VPS as that name, not some . delimited FQDN or anything. That seemed to work, but I am not sure if I am missing something. I also want to make sure that I can't receive email in Postfix either. – Joel Marcey Jun 25 '09 at 21:40

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