During website creation on the Configure Service step not all account's domains are listed.
Why does it happen?
There are other services providing a mail service on the account, such as Hosted Exchange, Office 365, etc. Currently, domains registered in such services cannot be used with WebHosting Plesk. This behaviour will be improved in scope of the feature request PFR-70.
Please, contact your Technical Account Manager to trace the current status of PFR-70.