On 2018-01-03 14:36, Bill Cole wrote: > I have run an environment where each MTA node in the external gateway > layer would add a MID with its own FQDN to any message passing through > missing a MID. Those names could not be resolved in the world at > large, but they were absolutely valid and guaranteed unique.
This is what I do with my personal outgoing messages. Free 3rd level DNs are available at freedns.org and I use a bogus (from the DNS POV) 4th level name under one of those, distinct for each host, as the RHS in my Message-ID. There's no good reason to use "localhost" or "localdomain". -- Please don't Cc: me privately on mailing lists and Usenet, if you also post the followup to the list or newsgroup. To reply privately _only_ on Usenet, fetch the TXT record for the domain.
