If you want to receive emails on your PC and mobile and read them on both devices, you will need to use IMAP on all of your devices. POP should only be used if you only want to access your emails on a single device.

Hi Ben, Many thanks. What I still don't understand is why Mozilla is urging me to change. BW, David

Would you please share a screenshot of that message? It doesn't seem to be anything you would receive from Mozilla.

Hi David, Thanks for your interest. I haven't had any more requests from what I now assume were scammers, so I can't send a screen shot. I did give them some personal information but I can't remember how much. I am concerned that my computer is seriously compromised which may become clear at some point in the future. What would be a sensible course of action in the circumstances? Can Mozilla help? Thanks, David

If you think your computer has been compromised, I suggest scanning for possible problems. The free version of Malwarebytes can do a full scan for problems and delete them. It doesn't run all the time, only when started, but that seems to be what you need. I would also do a backup of critical stuff on your PC to be safe. Here are steps to backup thunderbird:

1. ensure thunderbird is not running
2. enter %appdata% in search window on task bar and press Enter key
3. this should open windows file explorer in Appdata\roaming folder
4. highlight the Thunderbird folder and copy to external media