You don't have it in Mailman 2 because the archive URL is assigned by the archiver, and there's no way to retrieve it at archiving time. In pipermail, a message's ID is history dependent (specifically, how many messages have been archived so far this month), so it's not possible to calculate it either.
In Mailman 3 there is provision for a permanent, well-behaved ID for every post (the message_id_hash), so it will be possible to add this feature for the default archiver (which is in the process of being written by Toshio IIRC).
You don't have it in Mailman 2 because the archive URL is assigned by the archiver, and there's no way to retrieve it at archiving time. In pipermail, a message's ID is history dependent (specifically, how many messages have been archived so far this month), so it's not possible to calculate it either.
In Mailman 3 there is provision for a permanent, well-behaved ID for every post (the message_id_hash), so it will be possible to add this feature for the default archiver (which is in the process of being written by Toshio IIRC).
I am pretty sure this bug has been posted before.