+++ This bug was initially created as a clone of Bug #1778317 +++

Maybe 21 years after bug 97854 was filed, we could just make this work for a more flexible UX. For bonus points after bug 1777913.

STR:

• New Address book, best seen in vertical layout (horizontal layout has no DnD yet, see bug 1777913)
• Have some contacts and a mailing list (empty suffices) in the same AB (e.g. Personal AB).
• Try to drag contact(s) from the AB directly onto the mailing list item in the same contacts/results list (vertical drag; red arrow in screenshot).

Actual result

• Drop forbidden (see screenshot, red arrow)

Expected result

• Drop allowed (more so given the current limitation where you can only have cards of the containing AB in a mailing list).

As a workaround, users can toggle the AB open to show the mailing lists in the directory tree and drag contact(s) from the list onto one of those (green arrow in screenshot).

Common denominator of the duplicates here is that users are failing to discover the horizontal drag to the mailing list node in the directory tree, which may not always be visible (see-also bug 1777754 is another duplicate). Looks like the direct, vertical drag proposed here is much more discoverable, and there's really no excuse why it shouldn't work.

Geoff, how hard would it be to make mailing list items in the contacts list a legitimate drop target?
Note the special case of All Address Books with cards and mailing lists from multiple AB's.

I don't think dragging items from a list onto other items in the same list is a good idea for just about anything. We're already adding more ways to add contacts to a mailing list which should be sufficient.