Event id 1021 when phoning a UM extension redirected to voicemail

By | 2010-08-19

We were trying to configure the UM role in Exchange 2007 and had to buy an AudioCodes IP gateway to translate traffic from the legacy PBX into SIP traffic for the Exchange server.
Very early on we ran into an issue where if we diverted a phone to the Exchange UM pilot number (i.e. re-direct all calls to voicemail) then if we called that phone we would get rejected.

A lot of diagnostics and tracing later, we discovered that the calls were being rejected by the UM server, and it was throwing a 1021 warning in the Application log. The message reads:
The Unified Messaging server rejected an incoming call with the ID "<call-ref-number>@<um-server-ip>". Reason: "The Unified Messaging server cannot find a valid UM hunt group for "<extension>" associated with UM IP gateway "<um-server-ip>"."

So the UM server was trying to find a hunt group for the extension that we were calling, and was thinking there wasn’t one configured. We did however have a hunt group configured! We had deleted the default hunt group on the ip gateway, and configured a new one with the pilot number as the pilot identifier…big mistake…

It turned out that when you configure a hunt group in UM, if you give it any Pilot Identifier number at all, that is the only number that it will be triggered for. So what you have to do is give it a blank Pilot Identifier! Trouble is you can’t do that, when you make a new hunt group the dialog will not let you create it without typing something in. So what do you do?

Well the answer is: delete and recreate the IP Gateway configuration object in the UM IP Gateways tab of the UM Organization Configuration section. That’s all you have to do! What happens is that when you create a new IP Gateway object it automatically creates a default hunt group with a blank pilot number – and that’s what we want.

Once you’ve done that you’ll be able to call the redirected phone and leave voicemail. Phew. Working UM system!

Lesson learned today: don’t configure things in UM if you don’t know what they’re for…