Why did you need to re-enter your password?

I rather think you haven't told us everything yet.

What does "we changed servers" mean? New email addresses? Or same email address moved to a different host?

POP or IMAP? I suspect IMAP since things went missing.

When I clicked on an email I needed it wouldn't load, and a pop up came that said "the IMAP server ****@1wps.net does not seem to support encrypted passwords. if you just set up the account, please try changing to 'password, transmitted insecurely' as the 'authentication method' in the 'account setting | server settings'. If it used to work and now suddenly fails, this is a common scenario how someone could steal your password."

When I switched to password transmitted insecurely, it asked for my password, and was I entered the password that is when all the emails deleted.

When I say I changed servers, I meant to say we changed host companies that host our emails. Same email but new host.

Yes, IMAP.

It sounds like you had all the old emails on original server and had in the past synchronised those folders to get emails.

Then you changed all the server settings to point to the new server. When you tried to access the mail on the old server, it came up with the new password because you were now pointing to the new server which of course would not have any of your old emails on it. hence all the emails 'disappeared'.

You should have synchronised all your old server imap folders to get a copy in thunderbird and then in offline mode, moved them off the server into Local Folders. then performed a backup of your Profile as the only copy was now in Thunderbird.

Then you could change the server settings to point to new server OR delete the imap mail account and recreate a new one.

At this point you could try pointing it back to the old server to see if you can get access, but if you did not get those emails off the old host server and you are no longer paying for it then they may be lost.