On Tue, 3 Jan 2017 17:30:39 +0100 Reindl Harald wrote: > Am 03.01.2017 um 17:20 schrieb RW: > > In practice all you need to do is use a different domain or > > sub-domain in the Message-ID, one that's never used in email > > addresses. Unless you are a large service provider it's unlikely to > > be abused, and you can turn-it off in seconds if it becomes a > > problem. > > in practice you have no control about the message-id at all since > it's generated by the MUA and *not* the server
It depends on the circumstances. Lots of admins have control over hostnames or can deploy pre-configured email software. There's also webmail where you do have control.
