> If you are mixing IPv4 & IPv6 servers in the MX list, it is important that > the MX list be set in the following manner... > > IPv6 only servers MX a > IPv6 + IPv4 servers MX b > IPv4 only servers MX c > > Where a < b < c No, this sort of ordering is only important if not all the servers can do "final delivery" (i.e., take the message out of the SMTP world).