Select File/Offline/Work Offline, or click the icon at the left end of the Status Bar. Then, File/New/Existing Mail Account..., enter your credentials, click Continue, click Advanced config. on the next screen and enter the settings manually. When you're finished, go back online.

Thank-You sfhowes, I have been fighting that for years, your solution worked great!

So I made a new Profile, and I copied all my old files into it, but they do not appear in Thunderbird do they need to be indexed or something?

Which files did you copy and where did you copy them? Are the accounts POP or IMAP. Note that with IMAP, folders that exist on the mail server will automatically be downloaded when the account is added to a new profile.

Hi sfhowes, sorry for my slow reply, I got interrupted, My accounts are IMAP, but they are huge, and I have an offline Archive for what I can no longer keep online.

I Keep my Profile in a special folder on a RAID doubled drive, in this case labeled simply eMail

I Installed a new Copy of Thunderbird on a New computer this morning and and in the server settings menu/Local directory with Browse, I was able to find all the files. that was early this morning, they all appeared in Thunderbird exactly as they were suppose to.

But I have 2 Accounts, the second one I found had been pointed to the default folder on C Drive, I tried to put this one in the same special folder I reserve for eMail.

I copied the Default profile for the secondary account from it's place on C Drive to my special folder, I might have overwrote something, because all my files vanished out of Thunderbird

I have since Removed and Reinstalled Thunderbird a couple of times and Overwrote the Data files from my backup a couple of times, I cannot reproduce The arrangement I had this morning early.

I have refused the Password manager my Passwords for these accounts as I fear a Mix of downloaded eMails and back-up eMails