Форум поддержки Thunderbird

My wife & I have the same PCs running Windows 10 & Thunderbird 115.11.0 (32bit).

We have a hosted web-site that also supports email, and we each have an email account (eg neddy@goon.com.au & minnie@goon.com.au). I've checked that both our POP server configurations are identical but despite that about once a week minnie@goon.com.au receives a warning to add security exception but neddy doesn't. This started happening two weeks ago after a years error free running.

The host has checked that goon.com.au has a valid SSL certificate, so what could be causing the discrepancy and how do I set about fixing it please?

I installed Thunderbird and downloaded the mail (IMAP server) to the mailbox, but at the same time the program deleted all the mail from the server!!! I can't find anywhere in Thunderbird how to turn it off so that the program doesn't delete messages from the server. Someone suggested that you should turn off "the selected folder will be available in offline mode" in the Synchronization tab. I did it, but it didn't help and I turned it on again. Now I don't have my messages anywhere, neither on my computer nor on the server. Rescue news from ten years - where are they????