Question

Setting up DNS with mail on Dreamhost; getting PHP to find the right mail server

  • Posted on January 2, 2014
  • jmillerAsked by jmiller

I’ve got a droplet running a site (let’s call it example.com). For a variety of historical reasons, the site’s domain is registered at Dreamhost, which is currently providing the domain’s DNS and mail service. This is working fine EXCEPT that the site (based on Drupal 7) is not able to send mail to an address at example.com – when I track /var/log/maillog, Postfix reports that the attempt to send fails because of an unknown user (yes, the user really exists in the Dreamhost mail system); this happens both when Drupal (php, really) tries to send mail and when I manually send mail from the shell via mailx. Outgoing mail from the site is in fact working, by the way; I can send to addresses other than example.com via both php and mailx. Finally, I’m not running a DNS server as part of the droplet.

So:

(1) How do I get the site to understand where its mail server is? I’d like to leave the mail service at Dreamhost for now, but I’m open to moving the DNS service to DigitalOcean if that makes things easy/possible.

(2) Once mail is working, I’ll want to set up SPF records for the domain. I guess it’ll be obvious where/how to do that, but that will be an issue down the road.

Thanks!


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This is one reason I don’t name my droplets as the parent domain (e.g. don’t name your droplet ‘example.com’). The default postfix configuration assumes that it should handle email addressed to the host it is on. Give your droplet a subdomain name (e.g. I use 'dosN.example.com - ‘do’ to indicate a DO host (I do have machines in the same domain on on other services), ‘s’ to indicate a server, and N is a server number. So my first DO server would be named dos1.example.com. Come up with your own naming convention - I use tolkien names on my home machines.). Then CNAME service domain names (e.g. www.example.com, ftp.example.com, smtp.example.com) to the appropriate host name, and put the appropriate A record on the domain root if, for example, you want your web site accessed without the www. If the droplet’s name is, e.g. dos1.example.com, then the postfix server running on it will assume that it handle emails for username@dos1.example.com, not for username@example.com.

OK, I think I’ve got this fixed. First, I’m really running postfix, the default mail agent for CentOS 6.4, which the site is running. Second, what I’m apparently trying to do is to set up postfix as a “null client”, which sends but does not receive mail. The definitive writeup on this is at http://postfix.cs.pu.edu.tw/STANDARD_CONFIGURATION_README.html , but http://starikovs.com/2013/03/02/config-postfix-only-send-mail was a bit more direct: /etc/postfix/main.cf needs to be edited to specify inet_interfaces = loopback-only and mydestination = Once I made those changes and restarted postfix, things worked appropriately: mail still worked, and mail to example.com used the Dreamhost servers as specified in the domain’s MX records. So far, anyway… <br> <br>

Looks interesting; thanks! But I think my real problem lies with the site not having a correct notion of where its MX servers are. msmtp looks like a replacement for sendmail, but I’m not sure that it would behave any differently regarding figuring out which server to talk to.