Further to my problem. If I move all emails from pop server to Trash from inbox they do not get pulled again into Thunderbird as new emails. So def some flags not being set properly in Thunderbird. Hope this helps

Further Investigations: After testing various scenarios I did some digging into the settings for each of the mailboxes I have set. Noted that the tick box for the main account was not set in the section regarding what to do with emails on the server - see image attached After setting this & doing additional testing the issue appears to be resolved. I will continue to monitor this issue for now

This is how mine have always been set and the accounts are still set this way, if I interpreted your image correctly. I'm getting emails downloaded multiple times a day and also every day until they are deleted from the server. Very frustrating.

Hi, the issue seems to be that the flags for how emails are treated to the external mail servers may have not been set correctly before the update. I found the box not ticked for the days left on server, it never had the problem before so could it have been a bug which was fixed, or the earlier versions ignored the flag box. Either way it seems ok now so am closing this now. Thanks for the reply

Hopefully that's your problem fixed, fingers crossed.

I deleted my mail fron the server a week ago and the new emails are still duplicating. Will check and double check the settings, but nothing seems to work so far.

Hi Tony, is the server using POP or IMAP. The issues I had were with POP servers. I connect to 2 pop mail servers & 1 IMAP, only the POP mail servers had the issue