For some SIP providers, the default configuration of DTMF detection, Auto (RFC 2833 / In-band), does not work. You must find out the correct method from your SIP provider and configure it manually.
This procedure applies to Kerio Operator 2.4 and above.
- In the Administration interface, navigate to Configuration > Call Routing > Interfaces and routing of incoming calls.
- Select the SIP interface and click on Edit.
- Go to the SIP Details tab.
- Select the correct DTMF method.
- Click on OK.
The desired DTMF for the SIP interface has been selected.