I used to have that same problem when my ex was deployed and I'm getting the same messages now.
I don't know if this is true or not, but sometimes ships and other places intentionally disable their email, especially when something 'big' is going on wherever they're at. Military personnel do that so that it won't compromise their location or whatever action is being taken.
Other times it could be that the server's being flooded with emails.
Threaded Mode