This is only True for Cerb4 4.1.x and 4.2.x. Starting with 4.3 They have upgraded to a new version of swifmailer 4.04 that is a diff syntec. Please see http://middleswarth.net/content/cerb4-adding-images-html-outbound-emails... for 4.3+.
Thanks
Robert
Cerb4 use swiftmailer to send emails. The files to change is api/app/Mail.php
More documention is avaible at:
http://swiftmailer.org/wikidocs/v3/composition/basics
Code snippet for finding group ID info.
$ticket_id = $message->ticket_id;
$ticket = DAO_Ticket::getTicket($ticket_id);
and then $ticket->team_id is the Group id.
// #### Inserted in there to add html part.
$answernet_body = ''.$message->body.'';
$mail->attach(new Swift_Message_Part(nl2br($answernet_body), 'text/html', 'base64', $message->encoding));