Mac Mail problems with IX Web Hosting

I am having problems with my MAC Mail client (10.8.1) on IX Web Hosting. During the last week none of my three domains has been able to access the IX Webhosting mail server. In the past, one or two of them might have a problem for a short time, but now none of them are able to make connection. I have talked to their people, but they just blame is on the Mac mail client saying that everything is fine on their end. However, they help me set it up in the first place, and it did work for a couple of months. Now it doesn't and they haven't been much help. Their Mac experience seem to be limited. Anyone have any ideas on how to make it work.