Each alias may redirect mail to several recipients, and each recipient may be one of the following :

Email Address
  Either a full email address like `foo@bar.com`, or the name of another user on your system like `jcameron`.
Addresses in File
  For this kind of alias you must specify the full path to a file containing a list of email addresses, one per line. Each address can be either fully qualified, or the name of another user on your system.
Write to File
  In this case, email will be written to the specified file. To have all email to some address thrown away, give `/dev/null` as the filename.
Feed to Program
  Each time an email message arrives for this alias, the specified program will be executed and the entire email message (headers and body) passed to it on the standard input.