Get two duplicate copies of each email.
may I ask what account does this happen on? Is it Gmail by any chance?
I’m using Gmail.
if you are using gmail labels like Important/Starred/All Mail then that is the cause of the issue. Gmail sends these through IMAP stream as separate emails and creates duplicates in eM Client. You can choose which data to send through IMAP stream in your gmail’s web interface in Settings > Labels where you choose which labels to forwards through IMAP. Just uncheck any of the unnecessarry categories.