Thunderbird to EM Client - disable uploading E-mails to server

Hi all, after continuous problems with Thunderbird and Yahoo I installed EM Client today.
Out of four accounts I used, one was IMAP the rest POP.
Important: I regularly delete old emails from my web mail accounts as they had been downloaded to Thunderbird already. That’s enough, I don’t want my web accounts to be congested with tons of legacy emails as the space might get limited.

For all four accounts I imported everything from Thunderbird to EM Client, i.e. also any old email that wasn’t present on the web mail servers any more.
After this, EM Client starts to sync all four accounts with the servers and actually uploads all emails it finds missing on the servers!
So any email I deleted previously on the mail servers is now shovelled back up from EM Client…

Is there a way to deactivate that?
I don’t need a bilateral synchronization. Downloading from the web accounts would be enough for my purposes.
Thanks for any help!

sounds like your previous POP accounts were set up as IMAP.
I suggest exporting the emails you actually want to keep into eml files, just to be safe that you don’t lose them.
Then remove the accounts you dont want to use with IMAP protocol and manually set them up again as POP.
In Tools > Accounts click New account, but instead of automatic set up choose Mail > Other. Here you can choose to have your accounts set up as POP and configure your incoming and outgoing servers.
Ideally, once you set them up, all your emails should be downloaded and erased again from the server. If they do not, load them back in from your eml files.

If I am wrong and the messages synchronized back even with a POP account, go to Tools > Accounts and check the POP tab for your accounts, scroll down to Server settings and check if the option to ‘Leave a copy of the messages on the server’ is ticked.