I may have a problem with my email MX records or perhaps my Postfix setup. As I am totally out of my depth I need help determine what is up.
I host several websites on a VPS setup via Virtualmin and running Ubuntu 10.4LTS. One of the sites publishes a periodical newsletter. The previous newsletter sent in Feb 2013 worked fine but the most recent has about 10% of recipents bouncing back with a varity of 550 errors. Some of these address are known to be working ok. I need a guide on how to trouble shoot this issue as I dont even know where to start.
some of the return messages are:
host mx3.hotmail.com[18.104.22.168] said: 550 Requested action not taken: mailbox unavailable (in reply to RCPT TO command)
host extmail.optusnet.com.au[22.214.171.124] said: 550 5.1.1 firstname.lastname@example.org: Recipient address rejected: User unknown in virtual mailbox table (in reply to RCPT TO command)
host mx.syd.iprimus.com.au[126.96.36.199] said: 550 #5.1.0 Address rejected. (in reply to RCPT TO command)