I received a daily mail report with an error I find weird. Is the email address listed in the error message below, the sender or the recipient? I assume it should be the sender address since it doesn't make sense to list the recipient when the error occur on the sender. However, the sender is our colleague and how is it possible that our own domain is not found? Please enlighten me.
2010-01-21 10:45:51 deferred (host rxmail3.lga.net.sg[18.104.22.168] said: 450 4.1.8 <firstname.lastname@example.org>: Sender address rejected: Domain not found (in reply to RCPT TO command))