Jennifer, you have to call the guys who manage your mail server (the whole server thing, not only the software that run on it).
They definitely can help you, it's the same thing that we do with our customers.
Did you go directly to Newtek when you purchased the mail service or do you have an IT consultant who manages everything?
In the second case you have to call this consultant, not Newtek.
Unfortunately, I believe that the problem is at the server level (as often happens in these cases) and that it does not concern SmarterMail at all.