Форум поддержки Thunderbird

I have 4 e-mail addresses and corresponding inboxes. One is my personal addy that I use for most legitimate business. The other 3 are leftovers from former businesses and a spam addy. I use those other 3 addys sparingly, but only for sites I want to maintain distance from, and any I suspect might be spammers.

Thunderbird has worked wonderfully for me for some years, but recently, I have been getting duplicate messages in 2 of my 3 dummy accounts for every one that is legitimately sent to my main account. None ever show up in that 4th account, but I did just receive an e-mail that was intended for that 4th account, and the inbox acted as it should (no duplicates anywhere).

I have spent a couple of hours with a very dedicated service rep from my ISP, and she was unable to find any solution. She suggests that reaching out to Firefox is the next logical step.

My Thunderbird email on my PC will only open intermittently in the last few days. Re-starting my computer sometimes helps, but only temporarily. There are no error messages- just nothing happens. I am still able to access email on other devices - just not on PC - which I use a lot. I'd be grateful for ideas of how to fix this. Thank you, Pam Rycroft