Which configuration on Cisco UCM is required for SIP MWl to work?

The line partition must be inside the inbound CSS assigned to the CUC SIP trunk. This ensures that the SIP MWI messages are sent to the correct destination.

The other options are incorrect because:

Assigning an MWI extension on the mailbox is not required for SIP MWI to work.

The line partition does not need to be inside the rerouting CSS assigned to the Cisco Unity Connection SIP trunk.

Setting the "Enable message waiting indicator" on the port group is not required for SIP MWI to work.