3300 Drops Certain Calls From Exchange 2010 Autoattendant

[NickAdamhscc]

Hello,

I am using exchange 2010 as voicemail server for mitel 3300.

When user call main line exchange autoattendant answers and caller types in extension.

This does not work when an extension has DND or call forwarding enabled.

In this situation the call is just dropped.

Looking at a packet trace the Exchange server is sending a SIP REFER to the 3300 but the Mitel just drops the call.

This only happens from external callers, if I call the autoattendant from my desk and then dial an extension that has DND enabled the call goes to voicemail.

Does anyone have any suggestions?

Thanks.