Tonight I got several calls from people telling me that emails to one of my company’s domains were bouncing. I had been fiddling with some of the DNS settings and apparently (after half an hour of searching on the internet) this screwed things up.
As I learned, CNAMES override must other DNS records and a CNAME conversion is done even before an MX lookup.
At first, I had A records for both remotion.biz, www.remotion.biz and *.remotion.biz, pointing to my web server. I then removed the remotion.biz A record and changed it into a CNAME (pointing to www.remotion.biz). I left the MX records as is and thought this would work.
But, like I said, after researching online for a while, the CNAME overrides all other records. So if a mail server is looking up the MX record for remotion.biz, it first does the CNAME conversion, causing it to search for an MX record for www.remotion.biz instead of remotion.biz. And since no MX record for www.remotion.biz exists, things went sour!
Well, I quickly changed things back and after the changes had propagated everything was back to normal.
I’m happy I made this mistake on a lazy Sunday afternoon. Now it was only 3 people calling, instead of 20, which it’ll probably be on a busy weekday.
