Been using and loving Thunderbird for over 10 years - now on 115.18.0 (32-bit) with 8 different email addresses, all on 'ionos.co.uk'. My AV is Norton and seemed to 'upgrade' to 'Norton for Gamers' 2 days ago. Since then attempts to read messages get a pop-up window titled 'Add Security Exception' with text 'You are about to override how Thunderbird identifies this site. Legitimate banks, stores will not ask you to do this. ' It gives location as 'imap.ionos.co,uk;993' then a line says 'This site attempts to identifiy itself with invalid information'. Clicking button marked View shows details that include 'Organisation: Norton Web/Mail Shield' hence my suspicion. I've had a lengthy call with Ionos support, very patient and helpful, checking things at their end, concluding nothing of theirs has changed and all is working correctly. I tried one of the addresses using their webmail, which worked perfectly. About the same time that this happened, I started getting pop-up messages from Norton when I started software programs that I wrote myself some years ago. That's never happened before! Tried reading Norton help pages but cannot get hold of a human. Has anyone else had this problem? Should I ditch Norton? Many thanks!