Mail aliases allow us to define alternative names for users or groups of users. Each alias consists of a name and an associated array of one or more user names. They are stored in a file named /etc/mail/aliases. Historically, this was named /etc/aliases, and in fact a link still exists to allow /etc/aliases to be used.
It's useful to create aliases for many reasons, some of which are listed below:
Aliases allow us to provide a consistent look to our external email addresses, regardless of the login name assigned to each user. We'll use them to provide an external address for all users to allow them to receive email using a “firstname.lastname” address.
We can make allowances for names that may be easily confused or shortened. For example, ...