Synopsis:
   on [<modes>]mail [<serial#>] [-|^]<match> { <action> }

Description:
   This hook is triggered whenever the client detects that the user has new
   email locally.  It relies on MAIL being non-zero.

Parameters:
   $0    number of new email messages
   $1    total number of email messages in user's mailbox

Examples:
   To keep the new mail message grammatically correct:
      on ^mail "*" {
         echo *** You have $0 new message${[$0] > 1 ? [s] : []}, $1 total
      }

See Also:
   set(4) mail

Other Notes:
   This hook has no control over the extended output given when MAIL is set
   to 2.