Newly created user cannot receive email from outside our domain.

We are currently running Exchange 2003 R2. All users up to this point have not had an issue with sending or receiving email. The users are using Outlook 2010 to manage email. Recently, when creating new users, there is an issue with them being able to receive email from outside our domain. They can send outside and they can send and receive mail inside. This has been an ongoing issue. I thought it might have something to do with the size of the mail store since that was one of the errors I found in the event log (mail store is 30GB and you are trying to use 34GB). I cleaned up the mail store, cleaned out temp files, cookies... and rebooted the Exchange server. Verified the mail store was down under the 30GB and had the users in question try again. They are still not able to receive outside email. I found the registry entry that I changed for the size of the mail store. Still nothing. I am out of ideas and running out of patience. I have found nothing that will help in the forums to date. Any ideas would be greatly appreciated.