After doing some recherche on IMAP handling in Thunderbird, I decided to ignore milestone V 1.94 (IMAP-stored attachement as remote target) — for now. Instead I focused on V 1.95, V 1.96 and V 1.98 and revised the start-up script. Automatic synchronisation is now also possible at shutdown. And the synchronisation behaviour itself is tunable down to the processing/filtering of individual properties. Of course, each addressbook can be configured individually.
That led to the development of a new preferences dialog. Screenshots of the prototype are shown below.