We've recently run in to a problem with some external users trying to email some of our distribution lists. The following bounce message is sent to them:
This message was created automatically by mail delivery software. A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed: distributionlist1@domain.com host smtpserver.domain.com [xxx.xxx.xxx.xxx] SMTP error from remote mail server after pipelined sending data block: 550 5.1.1 User unknown distributionlist2@domain.com host smtpserver.domain.com [xxx.xxx.xxx.xxx] SMTP error from remote mail server after pipelined sending data block: 550 5.1.1 User unknown distributionlist3@domain.com host smtpserver.domain.com [xxx.xxx.xxx.xxx] SMTP error from remote mail server after pipelined sending data block: 550 5.1.1 User unknown
The Default Frontend Transport Service logs show the following:
rcpt to:<distributionlist3@domain.com> 250 2.1.5 Recipient OK DATA 354 Start mail input; end with <CRLF>.<CRLF> Tarpit for '0.00:00:05' due to '550 5.1.1 User unknown' 550 5.1.1 User unknown
Any ideas?