Aliases are different names for the same mailbox. Mail can be redirected from a generic department name to a real person. For example, you can redirect sales@yourcompany.co.nz to your sales manager's mailbox, or marketing@yourcompany.co.nz to your marketing manager.

Alternatively, you might want several departments each with their own mail address but you might only want to check one or two mailboxes. You can use e-mail addresses like sales@yourbusiness.co.nz, info@yourbusiness.co.nz, and tech@yourbusiness.co.nz which will all point to your default mailbox.  Or sales@yourbusiness.co.nz and marketting@yourbusiness.co.nz could go to one mailbox while webmaster@yourbusiness.co.nz

Aliases can be a very useful tool but it should be noted that the mail for all the alias accounts is effectively mixed together which is why mailboxes have advantages too.