one of the documented procedures in this installation of the ACS
bulkmail_send   bulkmail_id   user_id   to   from   subject   body   { key_code "" }   { extraheaders "" }   { bcc "" }
What it does:
Add a message to the bulkmail queue
Defined in: /web/philip/tcl/bulkmail-utils.tcl

Source code:

    if [empty_string_p $extraheaders] {
	set extraheaders [ns_set create extraheaders]

    # We want to make it possible for a custom key_code to be used
    if [empty_string_p $key_code] {
	set key_code [bulkmail_key_code $bulkmail_id $user_id]

    # We want to build our own reply-to
    ns_set idelkey $extraheaders "reply-to"
    set reply [bulkmail_reply_address $key_code]
    ns_set put $extraheaders "Reply-To" $reply

    # We also need to get the envelope sender
    set sender [bulkmail_sender_address $key_code]

    set message [bulkmail_build_message $bulkmail_id $user_id $sender $from $to $subject $body $extraheaders $bcc]

    bulkmail_queue_message $message