On 24 May 2017, at 9:25, D'Arcy Cain wrote:
I have no server called nan.vex.net
But your DNS says that mail for any addresses @nan.vex.net that might exist are handled by mail.vex.net, regardless of whether that name represents an actual server or whether mail.vex.net actually can handle those addresses. The same is true of any hostname under vex.net, implying a wildcard MX record.
I expect that you have or at least have had a reason for that wildcard record but you may want to reconsider it.
