Question
Is it possible to have a separate external web/mail server in Plesk?
Answer
Currently, there is no built-in Plesk functionality to manage external web or mail servers as service nodes.
It is possible to configure an external mail server. Note that in this case, all maintenance and management tasks (creation of mailboxes, configuring SPF, DKIM, etc.) should be performed on the external server without involving Plesk functionality.