For a while I’ve known that (legitimate) outgoing email messages originating from my web server were occasionally not reaching their intended recipients. I also knew that there was a DNS change you could make to help prevent this problem, but I didn’t know any more about it and it was a marginal enough problem that I could just put it off.
Finally today I decided to deal with it. And I was (re)introduced to the SPF acronym. No, that’s not Sun Protection Factor, or Spray Polyurethane Foam, or even Single Point of Failure (although in my case perhaps that last one is accurate). No, it stands for Sender Policy Framework, and it’s an add-on to the core capabilities of DNS that provides a way to positively identify the originating servers of outgoing email messages.
My situation is simple: I have a domain name that needs to be able to send mail from either my mail server or my web server. Most of the tutorials I found for SPF were far too convoluted to address this simple arrangement. Then I found this post by Cyril Mazur which provided the very simple answer:
v=spf1 a mx ~all
Simply add the above as a new TXT record in your DNS zone file, and you should be set.