That could be. I'm not a DNS wiz and I've never run into this before so it makes me a little nervous. I won't know if it is causing problems until everyone shows up on Monday morning. That's not a situation that I want to be in. As of now all of my test emails to and from them have made it through without issue. Also, as of the last hour, the problem occurs much less frequently than it did. Maybe I need to be more patient.
It would be cool if someone else that is using MS for DNS could check and see if it is happening with them. I tried a domain from another post with the same issue but it looks like he has moved his DNS away from MS.