Like a lot of American Express customers, Kelly and I receive email notifications from the company. Most of the time, these emails arrive with no trouble. Occasionally, though, they mysteriously fail.

We run our own mailserver, so I checked the log files to find out what might be happening. I found Postfix logging this message (and highlighted the important part):

Aug 17 01:23:45 maestro postfix/smtpd[22090]: NOQUEUE: reject: RCPT from localhost[127.0.0.1]: 450 4.7.1 sppim501.ipc.us.aexp.com: Helo command rejected: Host not found; from=sppim504@welcome.aexp.com to=blahblah@blah.edu proto=ESMTP helo=sppim501.ipc.us.aexp.com

You see, I’ve configured Postfix to reject incoming email from servers that do not properly identify themselves. It’s been my experience that 99.9% of the time an email arrives from a server that doesn’t identify itself, the email is spam. American Express’s servers are part of the few legitimate servers which do not properly identify themselves as required by the email RFC. The host sppim501.ipc.us.aexp.com does not exist in DNS and therefore email from this server gets flagged as suspicious.

I’m hoping American Express gets its servers fixed but in the meantime I’ll have to create my own hostnames to keep their emails from bouncing.