Email alias is not a real email account. Instead it's an address that forwards all email it receives to another email account. For example, if you establish an email alias called [email protected] to go to [email protected], then all email sent to [email protected] will be automatically forwarded to [email protected] (In this case, 'info' is called an alias of 'johndoe'.)
You can also setup email alias to forward to multiple usernames or another alias.
This way, you can have unlimited email addresses to fit your needs with only a handful of actual email accounts.