Reply only takes current mailing list into account

The various mail views only seem to show the current mailing list.

This causes a problem when using the Reply function; Reply All is usually what is needed.

There should at least be some indication that the e-mail was sent to more than 1 list.
[I know that the mail source is available, but that is hardly user-friendly]

Start by tracing the mail views and Reply function described in the issue; no files, tests, or entry points are named. Determine how messages sent to multiple mailing lists are represented, then define a user-visible indication and verify that Reply behavior accounts for all intended lists.

Written by the indexing model from the issue text.