You can't import folders to an IMAP account, but if you right-click Local Folders, IET NG/Import mbox file, you will see a window as in the attached picture, that shows the options to import a folder with subdirectories.

Perhaps you can explain what you're trying to do as far as importing to 'the new email'. Is it a different IMAP account or an account on another computer?

https://addons.thunderbird.net/en-US/thunderbird/addon/importexporttools-ng/

Thanks for getting back to me,

Basically our current emails are on our cloud server and we're moving them to our VPS server. So the accounts will still be the same just on a new server, if that makes any difference?? Sorry!

You'll have to ask your system administrator to confirm, but if the accounts and server names are the same, except they refer to a different physical server, I don't see that you need to take any action, beyond possibly adding the accounts again after the switch.

Spoke to them (TSO Host) and they've said we have to backup all emails via thunderbird and recreate the email accounts on to the VPS, then let TSO know once we've done all of this, they then change some bits their end and we have to then import all emails back to our accounts.

All accounts are really easy except 1 that has a massive amount of sub folders (we're a doctors clinic) so just need to find a way of exporting the main accounts email folder structure etc.

Thanks again!

As far as backing up all mail, Tools/IET NG/Save all mail files, will copy your Mail and ImapMail folders from the profile folder to a folder outside of TB. This includes all mail for POP accounts and Local Folders (in Mail), and all mail for IMAP accounts (in ImapMail). So, once you have the accounts set up on the new server, the mail from the backup can be imported. I would expect the host admins. to copy the mail from one server to another so that when you set up the accounts again as IMAP, the mail folders are already available, so that only the folders from the Mail backup folder are needed.