I entered to say the same. Not only Supernova. I purchased a Thunderbird based client (Postbox) in thehope that they solved the sluginess and...same problem. A

I entered to say the same. Not only Supernova. I purchased a Thunderbird based client (Postbox) in thehope that they solved the sluginess and...same problem. Also, I have the feeling that the Windows version is slower than the macOS one.