Email arrived 1 week later than time stamp

Ok our company is running GroupWise 2012 SP1. I have a co-worker whom is pretty reliable and has very little in her mailbox so I have to think she is right. She claims that although the time stamp on the email shows it came in last week and it appears in her mail box bold with last weeks time stamp, that it just came in today. Is there a way to track what could have happened to it? She is receiving all other emails just fine.

Sincerely,
Ken