I had a similar issue with Interac notifications: all were showing A as the sender instead of the correct senders. Turned out there was a contact (A) in one of the address books with the notify@payments.interac address that was applied to all senders. Deleting it restored the correct names in all previous and future notifications.

Thank you. This fixed one of the problems - the senders are now correct. I still have the strange global search issue. Searching for "Interac" I get a list of supposed emails most of which turn out to be nonexistent, for example cactusrose@metanetwors.net, or very strange, like interactions@zorpia.com, with the name of Natasha attached. Of course, I do not use the Chinese zorpia.com. Clicking on any of them tells me nothing found. I would at least like to delete zorpia and metanetworks, but it seems impossible as they are not found. The only one that is reasonable is the link to the list of interac notifications, all attributed to Z no matter who sent it (and Z never sends money and searching for Z produces none of these. notifications). Searching the address book for "notify" or "interact" finds nothing, just like for "zorpia" and "metanetworks".

I remain puzzled.

To fix the search issue, try rebuilding the database:

https://support.mozilla.org/en-US/kb/rebuilding-global-database

Global Search is 'facetted', so it finds items like interactions@zorpia when you search on 'interac'.

For address books, try searching from Edit/Find/Search Addresses; it offers more granular queries. Press Alt if the Menu Bar with Edit is hidden.

I checked all address books and couldn't find anything, but when I put "notify" in the search box inside the address book window, up came exactly as you describe above! John Smith "notify@payments.interac"! Wow! Thank you so much! But do you have any idea how this occurred? Did John Smith somehow set this up as a hack of some kind, or is this something that Thunderbird is responsible for? I would think that it is the latter, since my "real" email provider shows the correct sender.