I've recently switched my email to Google's Postini service (literally only about 2 days ago). I've modified my MX records so that my inbound emails now go through their SMTP servers then get pushed to mine.
However, my Outbound emails from my Exchange server, as of yesterday, are not going out. I've not made any changes to my outgoing mail - they still go through the same smart host.
When I telnet to my Exchange server from outside of my network, the helo command works, and the mail from command is OK, but when I use rcpt to: <email> command, I always get the following message:-
550 Requested action not taken: mailbox unavailable
If I telnet to the Exchange server from inside my network (even on the server itself), when I use the rcpt to: command, I get
550 5.7.1 Unable to relay
Any ideas please? Nothing has changed on this server in the past couple of years, so I don't understand why it's doing this now!