Edit provide Mail for: and add all domains you need
Select the domain, click on the bottom Create an MX record for this host name
Click on + to add a new user.
These are Mac users. Set Email adress (this is for SMTP).
Right click on the user and select Advanced Options...
Add the Email adress as alias (this is for Postfix).
Go to Administer Domains. Allocate the domain you want to host with LINK.
Got to Basic Configuration.
Click on the icon on the right of the domain "Edit name server".
Change all mail related CNAME and MX entries to mail.example.com