Allow MX-less domains
Allow MX-less domains

Currently, palletjack2zone errors out if a domain lacks an MX. Since it's
perfectly reasonable to run a domain without an MX, check if one is defined
and just ignore it if not.

saab-simc-admin/palletjack,notCalle/palletjack,creideiki/palletjack,creideiki/palletjack,saab-simc-admin/palletjack,notCalle/palletjack