Can I oblige Mail.app to (ask to) send via BCC when sending to a large group?
Mail is notoriously difficult to script effectively - particularly when it comes to outgoing messages not created by the running script.


tell application "Mail"
  set _title to name of front window
  set mList to messages of drafts mailbox whose subject is _title
  if length of mList = 1 then
    set _msg to item 1 of mList
    if length of (get _msg's to recipients) > 5 then
      beep
      error "Too many To-Recipients!  Do you want to send BCC?"
    else
      return "Send_Normal"
    end if
  end if
end tell


Something like this can be used in conjunction with Keyboard Maestro or a similar macro utility to have the utility select the send-menu-item.

While you can use System Events to do this I find that it sometimes takes 3 or more seconds to launch on my machine if it's not already running, and you start wondering why your macro isn't working when it finally takes off.

Other caveats to this approach are that the message must have been saved at least once to be detected.

So what you want to do is possible but very hackish.

-ccs