TMS570LC4357: DCAN Message box ID and MASK

I have the DCAN module working fine...

I can set a message box ID, to say 0x400, with mask 0x7FF  and all I recieve is messages with ID 0x400...(of note, all the messages are from a SmartMicro Radar which sends "target ID's from 0x400 to 0x4FF (255 potential targets.).

If I set ID box to 0x401, mask 0x7FF, all I see is messgages with ID 0x401.

now...

If I set the mask to 0x700...message box ID = 0x400...I see ALL messages in the same MESSAGE/MAIL box with ID's from 0x400 to 0x4FF... 

Q:

How can I determine with ID is associated with the received message?

(example test I did).

I hook a kvaser onto the bus (no radar)...I run my code....(say message box ID= 0x400, mask=0x700)...I send 1 message over the kvaser with ID=0x400...I reveive the data (I can see it in the DCAN registers).

I change the message ID to 0x4AB on the message I send with kvaser( I also modify the data to correlate what I send with what DCAN sees)......I see that data sitting in the registers.

so....how can I strip the actual received message ID with the data received??

thank you as always......