Sven M. Hallberg wrote in
 <87ikvu9rgm.fsf@unruhe.p.khjk.org>:
 |Claus Assmann on Wed, Aug 21 2024:
 |> So if two people on the same system send a message within the
 |> same seccond they get the same Message-ID?
 |
 |Yeah. Just pick 16 bytes (128 bits) of randomness, print them in hex,
 |and be done with it. Anything else is needlessly fanciful.

One of the terrible changes in email practice as i see it.
I love to see date and time therein.
I think these 80 or what byte randoms that Gmail and such use are
totally brain dead and inhuman (to the eye), i see no value, there
is nothing "to reveal", but a lot to loose (imho).
I at least and for one see references "as such", and then IDs with
date give a clear impression even if the message is isolated.
Btw the next release of my little MUA will bring user choice; the
implementation is pretty straightforward and easy:

   message-id
       When set ‘Message-ID:’ and ‘Content-ID:’ MIME (part) will be
       generated (but also see from†, hostname†, message-id-disable†,
       stealthmua†).  If non-empty generation honours the given format
       string, which consists of normal text and expandable conver‐
       sions of a percent sign ‘%’ and a conversion specifier.  If un‐
       set or empty, or if results are shorter 10 bytes or without
       randoms ‘%Y%m%d%H%M%S.%r%r@%a’ is used.  Date and time are in
       UTC (Coordinated Universal Time).

       ‘%%’      Doubling avoids expansion.
       ‘%a’      Sender address, with ‘@’ replaced by ‘%’ because some
                 spam detectors trigger otherwise for unknown reasons.
                 If unavailable equals ‘%h’.
       ‘%d’      Two-digit day.
       ‘%H’      Two-digit hour (24-hour notation).
       ‘%h’      Either hostname† or the real hostname; if unavailable
                 equals ‘%r%r’.
       ‘%M’      Two-digit minute.
       ‘%m’      Two-digit month.
       ‘%r’      A base64-URL (RFC 4648) encoded random string of size
                 four (4).
       ‘%S’      Two-digit second.
       ‘%Y’      Four-digit year.

Now one might claim that ‘%Y%m%d%H%M%S.%r%r@%a’ is a user
nuisance, but except for graphical drag+drop boxes (ie out of
a list of possibilities, drag+drop to a "drop bin", likely being
also moveable within the "drop bin" (aka "a thing showing the
dropped things in sequence")) i would not know a better approach.

 --End of <87ikvu9rgm.fsf@unruhe.p.khjk.org>

--steffen
|
|Der Kragenbaer,                The moon bear,
|der holt sich munter           he cheerfully and one by one
|einen nach dem anderen runter  wa.ks himself off
|(By Robert Gernhardt)