Perhaps the host prior to the ones that had the error were doing recipient checking?
Nope, I got the error immediately after trying to connect, before it could even send EHLO. R's, John
M. From: John Levine Sent: Sunday, January 19, 2014 17:56 To: nanog@nanog.org Subject: Where does "Downstream server error" come from?
I had some problems with incoming mail that I tracked down to a configuration bug, two hosts on the same LAN configured to respond to the IP address of the MX. It's fixed now.
While it was broken, attempts to send mail on some other systems got "421 Downstream server error." That is not a message that any of my mail software sends (I grepped for Downstream in the code, it's not there) so I presume it's from some middle box.
Does anyone recognize the message, what produces it, and why? There was indeed stuff messed up downstream, but why turn it into a mystery error message?
R's, John
PS: I wonder how long it'll take for someone to suggest unhelpful configuration changes on my host to fix the problem.
Regards, John Levine, johnl@iecc.com, Primary Perpetrator of "The Internet for Dummies", Please consider the environment before reading this e-mail. http://jl.ly