MWI in asterisk 1.4.X


When does asterisk send MWI Notification? a put a file in /var/spool/asterisk/voicemail/[context]/number/INBOX dir but asterisk send NOTIFY

Reliably Transmitting (no NAT) to
NOTIFY sip:504080@ SIP/2.0
Via: SIP/2.0/UDP;branch=z9hG4bK72091a0b;rport
From: “asterisk” sip:asterisk@;tag=as1ac82914
To: sip:504080@
Contact: sip:asterisk@
Call-ID: 32997ef74e725cf36a98f04e275b8b2f@
CSeq: 102 NOTIFY
User-Agent: Asterisk PBX
Max-Forwards: 70
Event: message-summary
Content-Type: application/simple-message-summary
Content-Length: 95

Messages-Waiting: no
Message-Account: sip:asterisk@
Voice-Message: 0/0 (0/0)

I think that Messages-Waiting should be yes.