From your Mac you can install a profile for the Apple mail app to use to access your mail.coop account. Here’s how.
Log in to mail.mail.coop
Visit https://mail.mail.coop
Log in using your mail.coop username (for example myname@cooptel.net) and password.
Download the profile
On the website page select the ‘Email’ link where it says ‘Apple connection profile with app password’
On the ‘Opening mailcow UI.mobileconfig’ dialog box choose ‘Open with’ and click on OK
Find the downloaded profile
Go to System settings from the Apple menu
Choose Privacy & Security on the left and select Profiles on the right
Check for an existing profile
(For the email address you are installing)
You may have an existing profile for this email address. Here for example there is a profile already installed for a myphone.coop address under ‘User’.
If so, you should delete this profile first.
Click on the existing profile to select it and click on the ‘-‘ button
Select ‘Remove’ in the dialogue box that appears)
Then once you have removed any existing profile for this email address…
Install the new profile
Double-click the downloaded profile
Click on install
Confirm by clicking Continue
It’s done.