since I upgraded my moodle from 2.4.7 to 2.5.3 and to 2.6.0 it stopped sending mails and messages.
Error calling message processor email
line 226 of /lib/messagelib.php: call to debugging()
line 2142 of /message/lib.php: call to message_send()
line 151 of /user/messageselect.php: call to message_post_message(
only after renaming the original phpmailer and placing the one exist in version 2.4.7, the problem was solved.