On Mon, 2018-01-01 at 10:29 -0500, Bill Cole wrote:
> On 1 Jan 2018, at 9:59 (-0500), David Jones wrote:
>
> > I think some mail systems will keep the same message-ID per email
> > thread so your system must reject some replies.
>
> I have not seen such behavior in the past 20 years...
>
> Intentionally re-using another site's MIDs is so wrong that I'd
> happily
> make it break hard.
>
> HOWEVER, the idea of enforcing any standard on MIDs beyond gross
> format
> (e.g.: <[[:ascii:]]{3,996}>) on a system where the admin isn't the
> sole
> user is ludicrous.
I've had good success junking anything with one of my domains in the
message-id, where I know the mail isn't actually from someone in that
domain. That's a pretty solid spam signature.
Lack of any message-id is also significant, but sadly there are still
some real senders sending mail with no message-id.
