We have a new Exchange 2010 SP1 server with 8 accounts working correctly. There is a 9th account that is unable to send email to anyone inside or outside the organization, but is able to receive just fine. Additionally, this user was able to send mail post migration, this issue just started today.
In message tracking, I see messages from earlier today before the issue arose, however I don't see any of the test emails I've sent. I've been using OWA to get Outlook out of the way.
Lastly, return receipts of messages sent to her are actually coming through/back to the senders.