How to import data from Thunderbird into eM Client correctly?

Version 3.0.10057.0. First start of eMClient, probably corectly imported 26000 email and 8 accounts from Thunderbird 3.1.10. But after that emClient started download all old emails from servers. I stopped after 5.000 emails.
How to deduplicated emails? OR
How to remove emClient and correctly start again?

Because many new emails arrived, the needed way is correctly removed eMClient, install again and then without downloading old emails or how to deduplicated them?

I have this problem to. Any solutions? I have 40k emails and i really don’t want download it again.