Aaron, do you still encoutner this issue?

No, but it's been years since I've had any POP3 mailboxes in Thunderbird.

Aaron, thanks for the update.

Danny, you're a heavy user of pop. Do you also use notifications and can comment on the current experience?

Our laptops & tower PC have run TB since 2010 (maybe late 2009), and I have always used the pop-up alerts -- in fact, I didn't know they were optional. But, on each machine, I have only one IMAP account and it's under the one global inbox, so I can't isolate & switch around as far as the STR suggests.

TB has always re-displayed the few most recent arrivals chronologically when another new item alerts as it comes in. For example, Msg-1 alerts, then when Msg-2 arrives & alerts, Msg-1 will be displayed after it too -- and so on -- when Msg-7 comes in, Msg-6, Msg-5, and maybe Msg-4 will re-display. But I've never had the exact same block of arrival message(s) repeat themselves and cause multiple alerts (such as Msg-1, 2, and 3 -- then later, Msg-1, 2, and 3 again.) I also operate mostly with sound muted, so I rarely notice audio alerts anyway, and any repetition would be far less irritating.

Is this just Windows 7?

Yes, both machines are Windows 7 Pro / 32-bit.

(FYI, also running Norton 360 (and previously Norton Security or Norton Internet Security) on laptop. Tower ran Norton Security or Norton Internet Security until ~2019 when it was switched to BitDefender.)

I have both pop and imap, but I don't have alerts enabled, so I can't accurately comment on the STR given. But I think if this bug still existed users would be up in arms. I

Gene I believe you have both imap and pop. Do you also have new mail alerts enabled and see the alert when doing step 6 of comment 0?

I don't have checks for new mail (at start, biff or idle) enabled on any account. I just click on inbox when I want to check for new mail. Since most of my accounts are just for test, this avoids lots of clutter when recording logs. Also, I only have one pop account, also just for testing, that I haven't used since pop got changed over to JS.
I'll leave NI set and test this out a bit later.

Ok, got a NI reminder and just now did the test. I only see one incoming message alert for the pop3 account when parked on inbox of an imap account. Selecting inbox of pop account doesn't produce another alert. (This following STR of comment 0 on linux.)