Originally I had my resolvers set to my own Dns nameservers. But I wasn't sure if this was correct, so I ask my hosting provider what they should be set to, they gave me their dns servers, and I changed it over to them, adding my namserver as third.

Then all of my email started failing to sent in or out bound. Why would this change cause that?

I reset the resolvers back to what they were, and things are now flowing properly.