Most often, a mail forwarding loop prevents you from receiving any mail, causing mail sent to you to bounce back to the sender. However, if you receive many copies of every email message, a forwarding loop may be the cause of this as well.

Greetings, James

Thank you for your reply. How do I deal with a "forwarding loop" to avoid the problem ?

You need to check with whomever is your email provider and ask for help on why it's doing duplicate emails. Firefox is just a Browser to get to the email service provider.

I contacted my service provider (Bell), they claim the problem is with Thunderbird email. I was guided to their Bell email where there was no evidence of any duplication of messages. I would appreciate assistance to eliminate the duplication problem.

I have this problem too and it only started about a month ago when I upgraded Thunderbird to a new release.

My email comes from my own email accounts hosted at X10Premium and there is only 1 copy of each email on the server (I leave them there for 7-14 days after they arrive as a backup).

It seems Thunderbird is now reading and downloading the emails, marking them as read on the server, but then regularly re-downloading them, so I have multiple copies of every email until it's deleted from the server.

It's also sometimes downloading 2 copies at a time.

Nothing has changed on my server as far as I am aware and this is happening on every account.

It's very frustrating and I hope the problem can be identified and fixed soon. Happy to provide any information that might help.

I recently had a similar issue but only on one email account. My Hotmail. I just clear out over 900 emails. 260 of the same copy from Team Vivaldi. 110 from another service. So on. And now it's starting to build up again. This is ridiculous. The attached screenshot shows 110 copies of the same email.