We have issues here pretty regularly when we are dealing with companies that host their public DNS with Go Daddy. It seems like Go Daddy always puts the lowest MX record at preference 0. My understanding of preferences is that they should be a positive number and 0 indicated that they did not accept mail at that location.

I've worked with several companies we do regular business with to have them get Go Daddy to change it to a preference of 5 and it immediately starts working.

We are running GroupWise 8.0.2 and routing mail through M+Guardian (2008.4).