Bug: subscribe button assumes that the mailing list has a -subscribe sub-address

The mailing list subscribe button is created by converting list@host to list-subscribe@host.

Whilst this is true for ezmlm (as used by the ASF), it may not be true for all mailing lists

Start by tracing the mailing-list subscribe button described in the issue and the code that converts list@host to list-subscribe@host. Determine how subscription addresses are supplied for lists that do not use ezmlm, then verify that the button no longer assumes that suffix and that existing subscription behavior still works.

Written by the indexing model from the issue text.