None of the above events will work, That warning is generated by FreePBX on the context
from-sip-external - Code: Select all
exten => s,n,Log(WARNING,"Rejecting unknown SIP connection from ${CHANNEL(recvip)}")
when you have set the options allow anonymou calls to NO and allowguest to Yes. There is not especial event associated to this warning.
You will need to catch all events that occur when you got this type of calls and do some kind of filter