I have several mailing accounts configured on Thunderbird, two of which no longer exist (from institutions of which I’m no longer a member). I don’t wish to delete these, as they can still come handy when finding old messages or adresses of old contacts. I just edited the settings to stop fetching messages, but I still get notifications saying Thunderbird failed to connect to the server. It’s a very minor inconvenience, but I’d rather Thunderbird not waste ressources trying to connect to them every time.

So, how’s the standard way to deal with accounts that no longer exist but of which you’d rather keep the already existing mails and data?