On 31.08.24 14:18, Kirill A. Korinsky wrote:
> On Sat, 31 Aug 2024 11:12:24 +0200,
> Stuart Henderson <stu@spacehopper.org> wrote:
>>
>> It is standard in most MTAs (including opensmtpd) to add missing
>> Message-ID at least to emails which they consider as locally originated.
>> (Doing this for mail from external origins risks DKIM failure with some
>> header signing setups).
>>
> 
> More of that. RFC 6409 requires that the MSA should add Message-ID, or
> replace it when it is invalud, see Section 8.3.
> 

Thanks a lot for mentioning this. I remember there were a lot of issues
with illegal message ids back in the days so that a solution needed to
be found. Just one example from the top of my head:

<https://bugzilla.mozilla.org/show_bug.cgi?id=54540>

Opened 24 years ago. Closed 22 years ago.

It really generated <nospam@nospam> as a message id (not to mention
Outlook Express etc.) and MTA authors started to take action to do
something about it because there were so many invalid/illegal non-unique
message ids in use. That's also one of the reasons for splitting MTA and
MSA.

-- 
Christian