I love to use macOS mail app, it works great from the point of view of a desktop app, it looks and behave as intended but is definitively not perfect. There are some features that would make it perfect.
One problem that I have with Mail.app is that does nothing if it is not open. So you get your mail until you open the app. Then, when you open the App you have to wait until the messages come and the list of items gets updated. Is not that much time, but it happens. I would be great that as soon as you open the mail app all your messages be right there.
Another issue is that you have to keep the mail app open (even if it is just hidden or minimized) in order to get notifications. So, lets assume that you forgot to open the Mail app in a while, and then an important mail comes in, you won’t get it because the notification didn’t show up.
Some may say, it’s nice because you don’t get bothered by a bunch of notifications, well, there could be an option to shut down the notifications if the app is not open. Or even better, have a list of VIP contacts (like favourites in iOS) that raise that notification, everyone else don’t.
If you want to send a picture or a file it would be good to have a share via email with a quick share “widget”. Even having just the composer would be good, but until now you have to load the whole Mail app in order to send a message. Curiously, you don’t have to do this to share to twitter. You don’t need to open the twitter app just to share a picture or tweet.
Mail app is great, I have tried several desktop mail apps, from Airmail which I like, Spark to some other much more simple like CloudMagic (when it was cloudmagic). I think Mail App just need some more love to be the perfect mail app.
BTW…, I don’t think the Mail app for iOS is as good as this one.