I am in the middle of a migration from SBS 2003 to SBS 2011. The migration is going fine and I have had no errors or problems thus far. I have already migrated user mailboxes to the new server and all users except one is receiving external mail. This user can receive internal email without a problem but not external. I have tested send emails from external email sources and I do not get any type of bounce back messages. I have checked mailbox size quotas and this does not seem to be the problem.
What else can i check, your help is greatly appreciated.