Incorrect... IMAP is synchronized. So delete a mail locally and it deletes from the server.

IMAP email is server based. All messages remain on the server and are viewed remotely when using an email client like Thunderbird. If you delete the message from a remote device it is removed from the server.

so to make sure I have this straight, when I had POP I could delete an email letter locally and still go and find it on the server but now with imap that email has voyaged into the ether?

Kind of depends on the provider. Gmail puts it in your All mail folder.

OK, I think I have a handle on IMAPs nature and I really do appreciate the help. now let me lay out my situation with greater clarity and tell you what i am now looking to accomplish.

I have a web based email client, charter.net, that just changed from POP to IMAP. They also went from having being Charter.net and Charter.com to just being Charter.com, combining the two. As part of the transition they went from POP to IMAP. Since that happened my emails no longer load in thunderbird. I tried removing them (charter) as my default email account and then re-installing them but that did not work. The problem seems to be that TB is telling me that my password or username is incorrect. Bear in mind that my old POP email was charter.net with it's unique password and my new IMAP email is charter.com with it's unique password. My goal is to get charter back downloading my email into Thunderbird. Can somebody help me?