With UGCS, you can have email sent to multiple different addresses delivered to your account. This way, you can have "throwaway" accounts for places likely to spam you- once you are done using it, you can remove the alias. We also use mail aliases as a way to keep track of other emails you use, so we can send you a new password should you ever forget yours.
Use the "mail_alias" command to add aliases. You can add them with
mail_alias addr1 [addr2 ...]
and remove them with
mail_alias -r addr1 [addr2 ...]