Thunderbird = TB. access your iDrive backup/copy, or access recovered hard-drive: • you MUST first '''make backup/copy''' of ALL sub-folders & files under this location, copy into another external drive: "%APPDATA%\Thunderbird\Profiles\" that is usually located here: "C:\Users\<YourWindowsUserName>\AppData\Roaming\Thunderbird\Profiles\" that "Profiles" folder ( ...\Thunderbird\'''Profiles'''\ ) contains multiple sub-folders , those sub-folders are various TB '''profile''' folders , a TB profile folder looks like this : "xxxxxxxx.profile-name" ''( where x in xxxxxxxx is random alphanumeric characters/letters/numbers, etc )'' ''( the "xxxxxxxx" is profile-folder-ID part , and "'''profile-name'''" is profile's name part )'' you can use the TB-profile again, with a new TB , but please first use exact same version of earlier TB, first . Later you can update/upgrade to what you want. your mail-accounts in TB, which were '''IMAP''' type/based , those emails are actually still in REMOTE MAIL SERVER . you '''did not lost''' those emails . TB just downloads a copy & then shows to you. once/when you (will) add those mail-accounts back (as IMAP based access) in TB, all earlier emails will re-appear. but, your mail-accounts in TB, which were '''POP''' type/based , those emails are DOWNLODED into your computer inside TB-profile folder by TB (according to POP specification). So those are not accessible anymore or '''lost''' , unless you have a '''backup'''/'''copy''' somewhere , or, if you have selected such options in TB : Do NOT delete/remove emails from remote mail-server after download a local copy , or , Keep a copy in remote mail-server. using online backup is '''not''' pro Privacy-Rights friendly , allows to increase abuse of human-rights , '''unless''' its locked (aka: encrypted) with such crypto mechanism, that ONLY you have/own the key , no one else have the (decryption/encryption) key . only that type of remote crypto/encrypted storage solution is better than remote plain storage , and still not one of the best. you should have used an external drive (locally) to make/keep/store your backup/copy. https://en.wikipedia.org/wiki/List_of_backup_software use data recovery software on you crashed hard-drive, to recover data. https://en.wikipedia.org/wiki/Data_recovery#List_of_data_recovery_software but what is right or correct for you , that depends on your choice/preference/convenience/expertise,etc,etc many factors.

2nd post.

hi THUNDERBIRD MOD/ADMIN , please add my earlier answer back here . this post can be erased . thanks. -[https://stackoverflow.com/a/64980413/3553808 atErik]