Troubleshooting the simple stuff

I was talking with one of my Barry pals recently and was treated to a rant regarding deliverability experts that can’t manage simple things. We’ve been having an ongoing conversation recently about the utterly stupid and annoying questions some senders ask. Last week, I was ranting about a delivery person asking what “5.7.1. Too many receipts this session” meant. This morning I got an IM.

Barry: I see your “too many recipients” and raise you a “DNS failure.”

Me: You’re joking.

Barry: “Unknown address error (‘550’, [‘REQUESTED ACTION NOT TAKEN: DNS FAILURE’])

Me: That seems pretty self explanatory. I would close the ticket with a “not a mail issue.”

Barry: It wasn’t a ticket. It was a direct mail to me by a very well known person on the sender side. You’d die if you knew who it was. But he didn’t send me anything useful, not even an IP address.

Me: You’re kidding? Please tell me you’re kidding. Please.

This is yet another example of people bothering Barry with questions that should be answerable by anyone who holds themselves up as a delivery expert. Really.
Barry is not your free consultant. Barry has a job and it does not involve troubleshooting problems on your end. Asking questions about stupid stuff like “too many recipients this session” or “DNS failure” is why most Barry’s don’t hand out their info to senders. They don’t want to be bothered with questions just because the sender is too stupid or lazy to do their own troubleshooting.
There are two things that come to mind immediately when I see this error message and two things that I would check before even considering contacting someone.

1. This is an internal DNS failure and the MX lookup on the sender’s side failed. The sender should do a manual DNS lookup and confirm they can get a MX record (or A) record for the recipient domain.
2. This is a DNS failure on the receivers side. A little harder to troubleshoot, but some ISPs check the DNS of the sending domain before accepting mail. Make sure that the domain exists in DNS and is answering queries promptly.

Once you have checked DNS and everything is OK you can move to the next step. Open up a telnet session to the mail server and do a manual SMTP session. Use the same Mail From: and Rcpt To: that generated the 550 you’re attempting to troubleshoot. You don’t need to do the whole session, just through Mail From: and Rcpt To:.
If the Mail From and Rcpt To: addresses are accepted by the receiver mail server, then go back into your MTA and resend the message that originally failed.
It works, you’re done. If not, go back and think about what else might cause a DNS failure, then test it. Same as you did above. Repeat.
EDIT: While writing the post, I heard back from Barry. The problem was that the sending domain did not exist in DNS. This issue would have been identified at the 2nd DNS check. No mail to Barry needed.