Defined in /secure/mail.h

/*
 * EXPAND_MAIL_ALIAS(a)
 *
 * This returns an array of all player-names (in lower case) that are
 * in the global mail alias 'a'. Notice that you _must_ check whether the
 * alias exists before you use this alias. You can use IS_MAIL_ALIAS(a)
 * for that. If you use this macro and the alias does not exist, you are
 * bound to get a runtime error.
 */
