Hi @homonto,
I haven’t used Thunderbird for a long time, but I quickly looked it up and it looks like their option for maildir should work okay (saving each e-mail in an individual file rather than having everything in a monolithic file). I wouldn’t expect much performance impact.
With sync, odrive is going to try to upload as soon as it sees a change, so you’ll just need to be aware of that in case there are any files that constantly change and need to be uploaded and re-uploaded. the maildir option should alleviate a lot of that concern, though.
The backup feature may be a better option for you since this seems to be a traditional backup use case instead of a full, bi-direction sync use case. https://www.odrive.com/features/backup