Email just got a bit more complicated for me.
host mx0.gmx.de[213.165.64.100] said: 550-5.7.1 {mx099} The recipient does not accept mails from 'monkey.org' over foreign mailservers. 550-5.7.1 According to the domain's SPF record your host '72.36.170.170' is not a designated sender. 550 5.7.1
The Sender Policy Framework tries to prevent spam and email spoofing. It lets the owner of a domain say "only these servers are allowed to send mail from my domain". Receiving servers check the origin of the email and if doesn't match, bounce it. Like above.

SPF doesn't really stop spam; most spam comes from made up domains. But it does give a way for legitimate domains to further legitimize their email. Maybe some day all non-SPF email will be treated with suspicion and then we can start working on blacklists of bad domains.

But for now it's all just a big headache for me. Using these awesome SPF tools I was able to figure out what was going on. Either I need to use monkey.org's official outgoing SMTP server (which brings authentication issues), get my little server added to the SPF list (which brings trust issues), switch to fully hosting my own mail, or switch to fully not hosting my own mail.

Another step to the end of SMTP.

Apparently the SPF records have been present for six months and I never received a single bounce. I wonder if some mail has been silently deleted though.
tech
  2007-02-20 17:00 Z