Asterisk 10.6 - Freepbx 2.10 Exchange 2010 & MWI

I am using FreePBX 2.10 & Asterisk 10.6 with Exchange 2010 - all is working ok except I would like to get MWI working with my Mitel 5340 phone. Can anyone point me in the right direction please.

Best Regards
Alan

Config & Wireshark trace of a user leaving a voicemail message for ext 8776

voicemail.conf
[exum2010]
8776 => 1234,Alan,8776@exum2010,attach=yes|saycid=yes|envelope=yes|delete=yes
sip_additional.conf
[8776]
deny=0.0.0.0/0.0.0.0
secret=password
dtmfmode=rfc2833
canreinvite=no
context=from-internal
host=dynamic
trustrpid=yes
sendrpid=no
type=friend
nat=no
port=5060
qualify=yes
qualifyfreq=60
transport=udp
encryption=no
callgroup=
pickupgroup=
dial=SIP/8776
mailbox=8776@exum2010
permit=0.0.0.0/0.0.0.0
callerid=Alan <8776>
callcounter=yes
faxdetect=no
cc_monitor_policy=generic

[Exchange]
host=192.168.1.12
type=peer
transport=tcp
qualify=No
port=5065
unsolicited_mailbox=@exum2010
context=from-trunk-sip-Exchange

SIP Packet sent to the Mitel phone from FreePBX

NOTIFY sip:8776@192.168.1.204:5060;transport=UDP SIP/2.0
Via: SIP/2.0/UDP 192.168.1.233:5060;branch=z9hG4bK404ca6b2
Max-Forwards: 70
From: “Unknown” sip:Unknown@192.168.1.233;tag=as0facd531
To: sip:8776@192.168.1.204:5060;transport=UDP
Contact: sip:Unknown@192.168.1.233:5060
Call-ID: 6af289d874ac42b7333ffe6b6e5d99ec@192.168.1.233:5060
CSeq: 102 NOTIFY
User-Agent: FPBX-2.10.1(10.6.0)
Event: message-summary
Content-Type: application/simple-message-summary
Content-Length: 88
Messages-Waiting: no
Message-Account: sip:97@192.168.1.233
Voice-Message: 0/0 (0/0)
**

SIP Packet Sent from Exchange UM to Asterisk

NOTIFY sip:8776@192.168.1.233:5060;user=phone SIP/2.0
FROM: sip:8776@192.168.1.233:5060;user=phone;epid=6A727C853E;tag=ae5635ce8f
TO: sip:8776@192.168.1.233:5060;user=phone
CSEQ: 26 NOTIFY
CALL-ID: 15cc3e2e35f04ddd894c9517956a111c
MAX-FORWARDS: 70
VIA: SIP/2.0/TCP 192.168.1.12:59847;branch=z9hG4bK924a715e
CONTACT: sip:8776@192.168.1.233:5060;user=phone
CONTENT-LENGTH: 100
EVENT: message-summary
SUBSCRIPTION-STATE: terminated
USER-AGENT: RTCC/3.5.0.0 MSExchangeUM/14.02.0318.001
CONTENT-TYPE: application/simple-message-summary

Messages-Waiting: yes
Message-Account: sip:8776@192.168.1.233:5060;user=phone
Voice-Message: 4/0 ***

I have the similar configuration as above. Asterisk 10 FreePBX 2.10 (upgraded from FreePBX 2.9 64bit).

I noticed that you can get a specific single mailbox MWI to work by specifying the Legacy Format

unsolicited_mailbox=4000 (For example)

None of the new forms below specified in the incident ASTERISK-17362 (new feature request for earlier version) Appear to work

Example

If unsolicited_mailbox=somebox@somecontext all unsolicited notifies will be delivered to somebox@somecontext
If unsolicited_mailbox=@somecontext the box from the sip notify will be used to deliver the sip notify to the specified box@somecontext.

Does anyone know

  1. If the Asterisk 10 development branched off before this new feature was added to 1.8?
  2. If an equivalent fix was added to the Asterisk 10 Code?
  3. If a separate Asterisk 10 patch is available for download?

Or anything else that needs to be done to make this work. I am very new to this so any help very much appreciated.