Once I run a search using the Search Messages window, how can I batch mark the >2000 resulting emails as read? I'm using Thunderbird 78 on a Mac running macOS 10.11 El Capitan. Thunderbird's Search Messages window (which is not at tab) returns the correct list of emails from many mailboxes. I can mark each INDIVIDUAL email as read by clicking the green dot in the search result's "Sort by Read" column. However, I have not found a way to mark as read a GROUP of emails, or all the emails in the search results. How do I do that? (In Eudora, emails in a Search list behaved like emails in a mailbox, and all the usual controls worked. Within Thunderbird 78's Global Search window, the M command does not mark emails as read either individually or in groups, and pull-down menus and their commands are unavailable.) Background: I'm a Thunderbird newbie, and a Eudora power user, doing cleanup after migrating 20 years of Eudora email in ~250 mailboxes to Thunderbird 78 via Mac Mail. Marking 2000 emails as read will be a 5-minute fix if I can get batch "mark as read" to work from the Search Messages window. (I would use a filter if I could batch filter my mailboxes. Unfortunately, I've only been able to make filters work by selecting one mailbox at a time. Running a filter on a folder containing mailboxes or subfolders does nothing. Filtering 250 mailboxes individually is gonna be slow.) (edited to correct terminology from Global Search (tab) to Search Messages (window), which is what I am using.)