Thunderbird/dovecot | upload emails from client folders to server

Installed YunoHost: (stable).


Can someone helps me to resolve this issue with my mail server:
After a power shortage my server wasn’t able to boot.
I decided to reinstall a new yunohost server.

As email client, I use Thunderbird.
This client has old emails that I want to upload back to the server.

For now, each time I update Thunderbird local profile with old emails, I can read them in proper account, folders and sub-folders.
But, as soon as Thunderbird connects to the server, all emails, folders and sub-folder are deleted and replaced by emails recently received on the newly installed server.

Long ago, I already upload old emails and folder from Thunderbird client to yunohost mail server without any trouble.

I am not too aware about imap protocol but I thought it was possible to upload emails from client to server.

Does someone knows how to solve this issue or has a link to a solution?

Thanks in advance.