[Andreas]

userdata_postsave

PHP Code:

if ($usergroups_changed)
{
    $pmdm =& datamanager_init('PM', $this->registry, ERRTYPE_SILENT);
    $pmdm->set('fromuserid', 13454);
    $pmdm->set('fromusername', 'Sendername');
    eval(fetch_email_phrases('usergroupschanged', $this->fetch_field('languageid')));
    $pmdm->set('title', $subject);
    $pmdm->set('message', $message);
    $botperms = array('adminpermissions' => 2);
    $pmdm->set_recipients($this->fetch_field('username'), $botperms); // Ignore PM-Box full
    $pmdm->set('dateline', TIMENOW);
    $pmdm->save();
} 


Adjust fromusername, fromuserid as you need and create a phrase usergroupschanged in phrasegroups EMail Body Text/EMail Subject Text - that's it