To set up a domain alias:
Domain aliases can comprise letters, digits and hyphens. Each part of the domain alias between dots should not be longer than 63 symbols.
Example: You have an e-mail address mail@yourdomain.com. You have set up an alias for your domain name, for example, alias.com. If you want to receive mail to your mailbox mail@yourdomain.com when it is sent to mail@alias.com, select the Mail check box.
When you set up a domain alias, resource records in its DNS zone are copied from the original domain name. This means that if your original domain points to an external mail server, your domain alias will point to that mail server too. However, to accept mail for the domain alias, the external mail server should be configured accordingly.
Whenever you change MX records in the domain's DNS zone, be sure to introduce the respective changes in the DNS zone of the domain alias.