one of the documented procedures in this installation of the ACS
im_email_people_in_group   db   group_id   role   from   subject   message
What it does:
Emails the message to all people in the group who are acting in the specified role
Defined in: /web/philip/tcl/intranet-defs.tcl

Source code:

    # Until we use roles, we only accept the following:
    set second_group_id ""
    switch $role {
	"employees" { set second_group_id [im_employee_group_id $db] }
	"customers" { set second_group_id [im_customer_group_id $db] }
    set criteria [list]
    if { [empty_string_p $second_group_id] } {
	if { [string compare $role "all"] != 0 } {
	    return ""
adde	}
    } else {
	lappend criteria "ad_group_member_p(u.user_id, '$second_group_id') = 't'"
    lappend criteria "ad_group_member_p(u.user_id, '$group_id') = 't'"
    set where_clause [join $criteria "\n        and "]

    set email_list [database_to_tcl_list $db  "select email from users_active u where $where_clause"]
    # Remove any html tags from the message
    regsub -all -nocase {<p>} $message {<br><br>} message
    regsub -all -nocase {<br>} $message "\n" message
    set message [util_striphtml $message]
    foreach email $email_list {
	catch { ns_sendmail $email $from $subject $message }