Add Mail User for Domain Admin - Plesk

Log in to Plesk by going to "https://mail.yourdomain.com:8334"

Replace yourdomain.com with whatever your domain is (ex. https://mail.johndoe.net:8334)

Your domain name is your administrator login (ex. johndoe.net)

After logging in, click on the "Mail" icon.

Click on the "Add New Mail Name" icon.

Enter the new email address you want to add to your domain in the "Mail name" field.

Enter a password for the new account in the "New password" field

Enter the same password again in the "Confirm Password" field to make sure you have entered it correctly.

Click "OK"

After clicking OK from the previous step, make sure the Antivirus option is enabled.
If it says disabled as shown below, click on the word "Disabled".

Click the "Incoming and outgoing mail" button

Click "OK"