Aliases are variations of an email address associated with a primary email account. Messages addressed to the alias address are delivered to the primary email account. For example, if the following:
joe.com@mydomain.com
joe-com@mydomain.com
joe_com@mydomain.com
are defined as aliases to:
joe@mydomain.com
then messages addressed to any of the above 4 addresses will be delivered to joe@mydomain.com. Messages addressed to aliases will still display the recipient’s alias address even though the messages are delivered to the primary account. Aliases do not count against mailbox plan limits or quotas.