Mail doesn't arrive in proper inbox

Hi.

A long time ago I tested Airmail. Did not work out.

I just use Mail on all my devices nowadays, the Mac running the latest Yosemite version and the iOS devices running the latest iOS 9.x versions.

I have several accounts, almost all seem to work.

But my main account (still Yahoo - will change that in this year), where I get my monthly schedules delivered to, has some ****** behaviour.

Most emails arrive without problems, but some emails don't get delivered into that inbox (just...

Mail doesn't arrive in proper inbox