(Ok, warning, this message is far geekier than my average blog post.)

I talked with someone who said he kept getting kicked out of a [yahoo group](http://groups.yahoo.com) he was in because his messages were “hard bouncing”. I’ll skip the discovery process, but in the end I found that some (?? Not all!?!) of the mail being sent to him from the group was using the DNS A record for his domain instead of the DNS MX record for his domain.

(don’t say I didn’t warn you)

WHAT??! the whole point of an MX record is to tell MTAs where to send mail. When I first learned about DNS 10 years or so ago, I recall that it was common to include a comment in a BIND configuration file before an A record that said: “For braindead MTAs that don’t understand MX records”. Now, ten years later, Yahoo suddenly has such a braindead MTAs?? What is going on?

And then… only sometimes?? In some ways that’s even more baffling. All I can figure is Yahoo has some new or old code running on one of its countless servers, and whenever it happens to hit that one, this problem happens. For most domains, the A record is the same as the MX record, so they probably don’t notice right away. But I sure hope they get a clue. I tried to send them one, but they sure didn’t seem to be welcoming it. My message about their MTA’s handling of DNS records is probably in a pile of queries about how to create new entries in an address book. *sigh* Maybe this blog entry will shame them into fixing the problem….