You could move them to a new Google account if there will be a period of overlap with both accounts available. This would be somewhat unusual so better to assume it won't happen.

The alternative approach would be to move all the messages you want to keep into Thunderbird's Local Folders account.

Maybe they will hand over your messages to Google and you won't have to do anything. But please don't bet on this possibility.

See next reply........

Hi Zenos,

Thanks for your comments - appreciated.

Current situation sees emails from the retiring provider being forwarded to Gmail now and all required emails in Mozilla are in the Local Folders now.

The place I wish to store the Local Folder emails is a new Gmail account which is currently "pending". When it's past pending and confirmed then both accounts will be open at the same time until the end of Oct. This account would be just used for these files and no new ones. They will be held for reference only.

Knowing that, can you please enlighten me on how to do the swap from Mozilla to the Gmail account??

Just as you did from the current account to Local Folders.

This account would be just used for these files and no new ones.

Thanks for your comments - I think I will go with keeping the Mozilla email app just to store the history files.