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.
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Download the profile
On the website page select the ‘Email’ link where it says ‘Apple connection profile with app password’
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On the ‘Opening mailcow UI.mobileconfig’ dialog box choose ‘Open with’ and click on OK
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Find the downloaded profile
Go to System settings from the Apple menu
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Choose Privacy & Security on the left and select Profiles on the right
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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
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Select ‘Remove’ in the dialogue box that appears)
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Then once you have removed any existing profile for this email address…
Install the new profile
Double-click the downloaded profile
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Click on install
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Confirm by clicking Continue
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It’s done.