privatemsg send message

In your own module, you need to get the user objects of both the sender and recipient.

There is a function called _privatemsg_send() it takes the following parameters:

_privatemsg_send($sender,$recipient,$subject,$message_body,$format,$thread);

$format I am not 100% sure on, but I have it set to 1 and that works fine.

To get the correct value for $thread I run the following:

$result = db_query('SELECT MAX(thread) as max_thread FROM {privatemsg});
while ($row = db_fetch_object($result) {
      $highest_thread_count = $row->max_thread;
}

//then add one to avoid your message becoming part of the wrong thread
$highest_thread_count = $highest_thread_count + 1;

That should help you out.