On 2021-09-21 at 12:25:30 UTC-0400 (Tue, 21 Sep 2021 10:25:30 -0600) Grant Taylor <gtay...@tnetconsulting.net> is rumored to have said:
> But why the penalty for using non-public addresses* in a Message-ID: string? Empirical evidence. The use of a non-public address in a Message-ID correlates to a message being spam. In my experience, so does using an IP literal of any sort in a Message-ID, but that may be an idiosyncrasy in my mail. > I was not aware that Message-ID had any requirements that the content had to > mean anything beyond being syntactically correct. As such I would expect > private / non-globally routed content to be allowed. After all, isn't the > purpose of the Message-ID to be a universally unique identifier? If so, why > does it matter what the contents is as long as it's syntactically correct? > What am I missing? Private IP addresses in general cannot specify globally unique devices (consider 127.0.0.1 or the very-popular 192.168.1.1) and therefore a Message-ID using an IP literal as the RHS part with a non-public IP cannot assure uniqueness.
