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 firstname.lastname@example.org to go to email@example.com,
then all email sent to firstname.lastname@example.org will be
automatically forwarded to email@example.com
(In this case, 'info' is called an alias of 'johndoe'.)
You can setup email alias so
that email is forwarded to an account outside of your domain
name as well. For example, you can setup
firstname.lastname@example.org to go to email@example.com.
This way, you can have unlimited email addresses to fit
your needs with only a handful of actual email accounts.