running Thunderbird 60.5.0 (32 bit). Have been running Thunderbird for years and know my way around settings fairly well but this problem is unusual. I have numerous other email addresses and all seem to work OK. This one in question was working OK (for for over a year on this PC) but very recently the Thunderbird account which is set to delete emails from server after download to PC no longer deletes emails from server and any new ones that are waiting (can see them on web mail OK). What we are getting now is numerous identical OLD emails (one or two) as these only are downloaded (not new emails) and not removed from server. Back quite while ago I had a odd problem with another account that also had been working OK. I couldn't find a ny way to rectify it so the Thunderbird account was deleted then re added and all worked OK. With this account there many very important emails and I suspect that if I remove the account these emails will also be removed which I can't have happen.