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 firstname.lastname@example.org. You have set up an alias for your domain name, for example, alias.com. If you want to receive mail to your mailbox email@example.com when it is sent to firstname.lastname@example.org, select the Mail check box.