Drop-down list can be tedious to navigate

If a domain has lots of mailing lists, the 'Other lists' drop-down can be tedious to navigate.
It would be useful to be able to filter lists that are no longer active, or present them separately from currently active lists.

For example, only show lists with posts in the last n months.
Or show older lists as a separate section after the recent lists.

Perhaps allow the user to select these options in the settings drop-down.

Start by locating the “Other lists” drop-down and the settings drop-down described in the issue. Clarify whether inactive lists should be filtered, separated, or controlled by a user setting, and define the recency threshold and expected behavior before identifying the affected implementation and tests.

Written by the indexing model from the issue text.