set mail-aliases

SET MAIL-ALIASES mail-alias [address] (same as DEFINE)

The MAIL-ALIASES variable is primarily used with the SHOW command.
  Type SHOW MAIL-ALIASES to display the list of all your currently 
  defined mail aliases.  

SET MAIL-ALIASES does the same thing as the DEFINE command.

For more help, type "help" and one of the following:
(at any prompt:)  save-init   set   show   define   who