Okay, I'll go step by step. I think you're best approach is to restore the profile first and then do the POP to IMAP switch. Here goes... - Since TB is already installed, you should see this folder setup in Windows File Explorer: - c:\users\<yourID>\appdata\roaming\thunderbird\profiles\

  copy your profile there, so that it is in the 'profiles' folder (actually, you can place your profile folder anywhere on computer that you wish. It's just easier for TB to locate here.) 

- start TB. It will prompt for an email id. Ignore that. Click the 'home' tab at top. - now right-click near top of panel and activate 'menu bar'. - now click help>moretroubleshootinginformation. - now scroll down to Profiles and click 'about:profiles' - the next screen should show yours. Click to activate it and TB should accept the accounts. At this point all is working, but some accounts are POP3 that you want to convert. Here are steps to convert: - Just create two IMAP accounts for the POP3 accounts, just as though the POP3 accounts weren't there, keeping email ids, etc. Be sure that, when done, there is an smtp server for each account. That is, if you have two POP accounts and two IMAP accounts, that there are FOUR smtp servers shown. At this point, you should be able to remove the POP accounts - tools>accountsettings>Account actions

Let me know how it goes.

Hi David,

Thanks for your help. The problem I'm now having is that TB is not showing the "old" profile. I can see it in the profiles directory, but it isn't on offer under troubleshooting or when I start with the -p switch. I know it's a working profile, because I can run it on my laptop. I guess I don't really understand the architecture. I have often copied this profile back and forth between desktop and laptop and never had a problem, so I'm assuming it has something to do with the new TB installation.

Any suggestions?

TIA Rebecca

Okay, assuming it is the desired profile, you can do this: - start with the -p switch - click the button 'create profile'

  step 1: enter a name to identify it, such as MYPROFILE  - this must be the first step
   step 2: click the browse button to locate and select that desired profile.  

close the screen and you should be done. Let me know how it goes.

OK, that worked, thanks so much! I am now at least back to where I started before the meltdown. Sorry for being dense, but can you confirm that this is how I change my primary mail from POP to IMAP? What I'm unclear on is how/whether I can create two accounts with the same e-mail address.

My primary mail address is mail@mydomain.com. It is currently POP3 with incoming mail going into a local folder inbox.

So in TB, I 1. Under acct/server settings for mail@mydomain.com, uncheck all the "check messages" boxes. 2. Create a new account with the same address, mail@mydomain.com and set it to IMAP. 3. Once I see that the IMAP mail@mydomain.com is working, I can delete the other (POP) mail@mydomain.com?

TIA, Rebecca

Yes, Rebecca, it's that easy. TB isn't looking at email id alone, but whether IMAP or POP, so you're good. But be sure to check before removing the POP accounts that you have an smtp server for each of the four accounts.

Thanks so much for your help!