Windows 2003 SBS SP2 running a small network of 12 WinXP clients, when I create a new user in AD everything seems fine, it asks if I want to create a mailbox for this user and the user/mailbox creation process seems to go smoothly with no errors. After I'm done creating the account I go to look at the mailbox in System Manager and it's not there. AD behaves as if the mailbox exists, as it lets me do the Exchange Tasks available in AD Users and Computers, such as move or delete mailbox. But Outlook 2003 clients cannot connect to the mailbox (I just get a message saying the Exchange Server is unavailable, even though I can ping it and browse the shares on the server). One other thing I noticed is that under POP Connectors for this storage group there are accounts set up for every user, and at least one of the users having this problem is also showing some POP retrieval errors in Event Viewer. However, I'm not real familiar with this part of the program so I don't know if this is related or not. This problem seems to be a recent one, as users created a couple years ago when this network was first set up have no problem accessing the server or their mailboxes. Only users that are being newly created in AD are experiencing this problem (3 out of 12 employees). Any ideas?

Sounds like the RUS isn't working. Also the mailbox isn't created until the user opens it with outlook. Check your recipient update service settings and update schedule.