I find myself often wanting to cite an email on the user's list in eg track tickets and usually want to provide a url to the email in the mailing list archive for this. Right now this requires me to manually navigate to the mailman archive (http://lists.einsteintoolkit.org/pipermail/users/) click on the relevant year and month and find the posting in question based on its subject line and author.
It would be very nice is the emails were tagged with a unique identifier that could then be used to retrieve it from the mailing list archive (and if this tag showed up eg in the footer that already contains the url of the listinfo page). One such identifier that may be available would be the message number (eg 003400 for http://lists.einsteintoolkit.org/pipermail/users/2014-January/003400.html). I have no idea how hard providing this would be though.