I’m totally new to this very interesting client. I’m using Protonmail as mail provider and until now I’ve used the native client. I’ve set up my accounts in em Client and so far so good, only problem I have every email from the proton mail account twice in my inbox. As you can see on the screenshot for the em Client forum activation email. It only happens with the Protonmail account. I’ve tried the same account within Apple Mail and it works fine.
See this following thread for multiple ways to disable the duplicate mail which can be done either via a “string in the account diagnostics tab” or via “disabling it in the Proton Bridge settings” or via “excluding the Proton Bridge All Mail folder” in the account setup.