No. That does not sound right.
Contact your hosting provider.
Ask them what it would cost to:
- Add a virtual host entry for the domain you want. In your example above you used: yyy.co.uk.
- Configure yyy.co.uk to receive email.
- Add your xxx username/alias/group to the mail system.
- And you can either use xxx@xxx.co.uk to your replyto field, use a group alias in your aliases file if using sendmail, or just add a .forward which points all email received at xxx@yyy.co.uk to xxx@xxx.co.uk.
It should take no longer than 15 minutes to complete the list.