Setup server admin email address?

[TechSpa]

Our server is setup as 'server.mydomain.com'. Of course, we are hosting our domain in plesk as 'mydomain.com' and a such, have email boxes 'user1@mydomain.com', 'webmaster@mydomain.com', etc.

Does anybody know how to allow the server to accept messages to 'administrator@server.mydomain.com' and forward them to 'webmaster@mydomain.com'?

Thanks in advance