Gotcha of the Day: EC2 + Postfix + Amazon Simple E-mail Service - Getting all three to play nice

I was delighted to see that Amazon's Simple E-mail Service has instructions for integrating with Postfix. In theory, this means you can configure Postfix once, and then all services on the system - be it cron, /bin/mail or PHP, will automagically work with SES.

Alas, I ended up tripping over one key part of the process. Whenever I attempted to send mail both from a verified user and to a verified user, I got an error from Amazon saying I was using an invalid address.

To debug this, I created my own little dummy mail delivery script like so:

!/bin/bash

##
## Debug script
##
LOG=/tmp/debug.log

echo "---------------------------------------------" >> $LOG
date >> $LOG
echo $* >> $LOG
echo >> $LOG
cat >> $LOG

I then wired this into postfix by changing /etc/postfix/master.cf to say:

aws-email  unix  -       n       n       -       -       pipe
  flags=R user=mail argv=/etc/postfix/ses/bin/debug-send-email.sh -r -k /etc/postfix/creds -e https://email.us-east-1.amazonaws.com -f ${sender} ${recipient}

Sending e-mail then dumped the command and output to /tmp/debug.log.

I realized that while the From: header was correct, the command line value of ${sender} was using the internal hostname provided by amazon. Something like:

  apache@domU-12-38-82-88.compute-1.internal

Amazon was obviously choking on that address.

But how to convince postfix to rewrite that address? Turns out, it's not so tricky after all. After much experimenting, I found that sender_canonical_maps would do the trick nicely.

I created a new config file: /etc/postfix/sender_canonical with:

 /(.*?)@(.*)/   $1@realdomain.com

And then added it to my main.cf with:

  sender_canonical_maps = regexp:/etc/postfix/sender_canonical

Now, when postfix receives e-mail from foo@invalid.internal it rewrites it correctly to foo@realhost.com and passes that to Amazon. Sure, I needed to verify apache@realhost.com, but once that was out of the way, I was all set.

Consider me a happy camper.