I host the domain dembowski.net and also handle the mail delivery. The mail ultimately ends up in Stefan’s house via his DSL line.
That DSL line has been prone to problems so I played with the idea of moving the mail to another server or VPS. But handling spam and keeping my web mail software up to date is a pain. So I wanted to move my whole domain to Google Apps for mail handling. Google is much better at distributed web mail systems and spam fighting than I am.
This was not universally accepted by all of my users. So I found a way to selectively send mail to Google Apps on a per user basis.
1. Sign up your domain for Google Apps
Okay, that one is a no brainer. I authenticated my domain by inserting a Google supplied CNAME record into my zone file. That established that I was the one in charge of my domain. Google lets you use it at no charge for up to 50 users.
In Google Apps I added another domain to my profile called app.dembowski.net. This way mail from Google gets delivered as email@example.com and Google will also receive mail for firstname.lastname@example.org.
2. DNS changes
I set up a sub-domain called app.dembowski.net. The DNS records for this domain are pretty sparse and only contain MX records that Google provides for users to point their domain to. These came straight out of Google’s instructions. In my zone file I bumped the serial number and added these lines:
app.dembowski.net. MX 10 aspmx.l.google.com.
app.dembowski.net. MX 20 alt1.aspmx.l.google.com.
app.dembowski.net. MX 20 alt2.aspmx.l.google.com.
app.dembowski.net. MX 30 aspmx2.googlemail.com.
app.dembowski.net. MX 30 aspmx3.googlemail.com.
app.dembowski.net. MX 30 aspmx4.googlemail.com.
app.dembowski.net. MX 30 aspmx5.googlemail.com.
Then I created a couple of A records for mail.dembowski.net pointing to two servers I run Apache2 on. More on this later.
3. Postfix recipient rewriting
The magic happens on my two Postfix MTAs. When the primary mail server goes down, mail queues up on my secondary mail server. It will stay there until the primary comes back. That sucks; last time we had an outage, the mail server was down for almost 24 hours.
The solution is to have Postfix receive the mail, rewrite the address to the sub-domain, and send it along for delivery.
In my /etc/postfix/main.cf file I added this line
recipient_canonical_maps = hash:/etc/postfix/recipient_canonical_maps</pre>
In the file /etc/postfix/recipient_canonical_maps I had something like this:
<pre lang="text">email@example.com firstname.lastname@example.org
This let me turn on Google mail handling on a per user basis. I ran postmap hash:/etc/postfix/recipient_canonical_maps and restarted postfix on my servers.
Now if my mail server tanks again, as long as the secondary is up, I still get my mail via Google Apps.
4. Lazy web mail URL
The two servers that are being pointed to as mail.dembowski.net? I created an Apache2 vhost on each one for that server name. In the root directory for the new vhost I created a small index.php with the following content:
header("HTTP/1.1 301 Moved Permanently");
I’m lazy. I can remember http://mail.dembowski.net easier than http://mail.google.com/a/dembowski.net.
Update: Or I could follow the directions and in my Google Apps dashboard just set a customized URL for mail.
After setting that up in my dashboard, I updated the mail.dembowski.net DNS record to be a CNAME pointing to ghs.google.com.
5. Test everything
Using an IMAP client (after I turned IMAP on in my Google Apps mail) I sent and received mail with my primary server’s postfix shutdown. That worked perfectly.
I also had other people in my domain send and receive mail just to make sure I did not bork that up too. All was good and we were all able to send and receive mail.
That’s it. As long as I create accounts in Google Apps and maintain the recipient_canonical_maps file, I’ve got a good solution for fighting spam with a good web mail client without impacting my other users.