If this is an Imap mail account: All folders in an imap mail account synchronise with same folders on the server which allows you to see emails. The emails are stored on the server. If you delete or move etc any email then the folder synchronises with server to update the server. The downloaded copy in an imap account cannot be considered as independent of server because the folders synchronise to only show what is on the server. Many imap servers offer IDLE which means they will push an email - server connects with Thunderbird and auto downloads the email.

If this is a POP account: Pop accounts do not synchronise with server. They get access to the server 'Inbox' and can download a copy of the latest emails. You have the option to download to pop Inbox and delete the copy on the server or set a setting that leaves a copy on the server. You can also set a setting to leave on server until you delete the email.

It would help to know what type of mail account you are using, Pop or Imap and also the server you are using eg: gmail, yahoo, comcast, BT etc.

When you download messages off the server, do you want a copy left on the server or not?

Do you only want Thunderbird to get messages when you select to 'Get Messages' and not check server when Thunderbird starts up?

Thanks for a fast reply, right now it's set to Imap. Mainly because I thought that's what I had to do. It used to be pop, I think they changed. I'm not sure if I have the option to use either. The server I'm using is Mindspring.com-Earthlink.net, I've been with them for about 22 years.

I used to(even back to Eudora) have it pull the messages off the server and delete them. About every 5 minutes(back when we used to use email for primary communication).

If you used Pop previously then you could download and delete off server as the folders in a pop account are totally independent of the server.

This is the info from the earthlink help page: https://support.earthlink.net/email/email-server-settings.php

Imap accounts work entirely differently and can only display what is available on the server. However, when I was looking into the mailspring site, it only seems to discuss imap: https://getmailspring.com/setup/access-mindspring-com-via-imap-smtp

Earthlink bought Mindspring, about a week after I signed up with Mindspring. That was in late 1998. How do I switch over?

You would have to create a new mail account for that email address. You cannot simply 'swap' any of the Account settings. New > Existing Mail account This time set it up as a POP account using the information at the earthlink help page. It will probably use Port 110, Connection Security: none, Authentication Method: Normal Password. Outgoing smtp use port 587, Connection Security: try STARTTLS, Authentication Method: Normal Password.

Thanks a lot, TH. It did the trick.