[Resolved] What does "550 Too many invalid recipients" mean?
...besides the obvious?
We were receiving the following error when our corporate mail server tried to send mail to any @shaw.ca address.
SMTP error from remote mail server after initial connection: host idcmail.shaw.ca [126.96.36.199]: 550 Too many invalid recipients
We checked the usual suspects - made sure we were not accidentally on any black list, checked to see if we had done any mass mailings recently (we hadn't) and triple-checked the spelling of the addresses we were sending to.
Hotmail and Gmail -> Shaw worked. Corporate mail server -> Hotmail and Gmail worked.
The problem went away while I was on hold with Shaw so we didn't get a chance to properly troubleshoot it. If anyone has some suggestions for what I should do next time, I would appreciate it.
We have phone service with Shaw and our system was accidentally configured to send an autoresponse every time Shaw sent us an email with our voicemail. I corrected this and the problem seems to be resolved.
Thanks to Alex and Nathan for helping me track it down!
m. -- Dear Obihai, please fix the FXS to FXO Relay in the OBi110. Add this as your signature if you agree!
Some mail servers will temporarily black list a mail server's IP address if it send too many successive e-mails to unknown addresses in that domain. It's a way to prevent dictionary attacks where they keep hitting the mail server with different e-mail prefixes at that domain until one matches a real user. It tries every word in the dictionary until it gets a hit.
It's a way for spammers to validate or harvest e-mail addresses for spam lists or to hack an account. Somehow it thinks your e-mail server is messing with theirs.