well it is pretty clear, the mail account does not exist. So perhaps you might provide us a clue as to why you think it exists.

I see it on the server, I see it in the program, I see folders. Where doesn't it exist?? We even have the folders saved and synced to the HD of the computer. Confussed????

coyotekw said

I see it on the server, I see it in the program, I see folders. Where doesn't it exist?? We even have the folders saved and synced to the HD of the computer. Confussed????

Well I am the one confused. "mail server for account (blah@blah.com) responded: Mailbox does not exist"

So clearly The server is telling Thunderbird it does not exist. Not that it can not connect, that it is connected and that mailbox does not exist.

Perhaps you have one of those awful anti virus programs that pretends it is a server as sends back garbage error when it looses the plot.

Or your server settings for the account are not right so you are not getting access to the folders for the account. But I certainly can not look at that. I am pretty sure blah@blah.com is you redacting actually what server is causing grief

Please add the troubleshooting information to your post To find the Troubleshooting information:

• Open Help (or click on three-line-icon and select Help)
• Choose Troubleshooting Information
• Use the button Copy to clipboard to select all. Do not check box "Include account names"!
• Paste this in your post.

Please also add the result of these troubleshooting steps to your post

• Does Thunderbird work in TB Safe mode (see Thunderbird Safe Mode)?
• Do you use anti-virus and firewall software? What is the version?
• Who is the email provider?
• What is the exact error message (verbatim)?