Probably a problem on the server end. One of my managers once had a problem with her account (i think she was on exchange as well) and it would send hundreds of copies of an email to people. And when those emails contained large attachments, there was little fun involved.
Yes, it was. If I was still getting hundreds of emails a day from her, I probably would not be here right now because I would have killed someone. I have no idea how it was fixed, as we work in different cities. I assume she contacted whoever manages their exchange server or email account.