Recently a working stand alone Exchange server stopped being able to send out messages. The messages arrive at the server (i.e. they are in the queue) but they are never able to leave the server and eventually return an "undeliverable" message with a #4.4.7 code (Problem with a timeout). Internal email (i.e. where the mailbox is on the Exchange server) is delivered just fine. I've checked all the "blocked" lists and we're not listed, the ISP isn't blocking anything, the domains are across the board and common (gmail, hotmail, etc...). Anyone have any ideas on what to check next?