How to re-synchronise emails received using pop protocol with server

Question

I have used Thunderbid with the same email address during many years using the pop protocol because I used to read emails on one device only.

Now I read them on multiple devices using imap, and I'm looking for a solution to synchronize back (or re-synchronize) old emails to other devices.

• I'm not looking for a solution for new emails, but for the already-donwloaded-with-pop emails that have been deleted from server, and are only stored locally on my computer.
• I'm not looking for a Thunderbid specific solution. I'm now also receiving emails with Geary on ubuntu and default android 6 mail application
• I'm now using the "do not delete from server" option for a while, but I haven't always did.
• My question is about my ISP email (French ISP "Free", domain free.fr, web access based on zimbra)
• Best solution would involve synchronize both received and send emails
• I keep emails organized in (too) many folders locally. And now I also have imap folders.
• I don't mind messing around with these folders and reorganize them after synchronization is complete, but it would be nice to also synchronize folders and keep my 15 years archive organized

Answer 1

Well, it looks like it was as simple as a "drag and drop" !

1. Add imap account next to pop account into Thunderbird
2. Drag and drop emails from pop account to imap account.
3. Done !

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