New to Nextcloud - I want to add the Mail app - but it's not available

Hello, I’m new to Nextcloud. I tried to add some apps, but I cannot add the Mail app. It doesn’t show.
How to proceed?

Did you add the new app store? And @ChristophWurst did you upload mail yet to the app store :D?

Is there a way I can do that manually?

You can download it here:
and install it in the apps-folder. Make sure the subfolder is called mail (sometimes it contains a version number).