Hi 张 舜毅,
The MB works the following way:
FLEXCAN_DRV_ConfigRxMb, this function configure the mailbox and the receiving ID, so only the messages send to this ID will be received.
FLEXCAN_DRV_SetRxIndividualMask, this function sets the RX mask, this mask corresponds to the following description:

So, only the bits sets are checked, for example, if you set this to 0 all the messages will be received, and depending of the bits set, the corresponding bits will be ignored of the ID.
An example, if you set the configuration like this:
can_buff_config_t buffCfg = {
.enableFD = true,
.enableBRS = true,
.fdPadding = 0U,
.idType = CAN_MSG_ID_EXT,
.isRemote = false
};
CAN_ConfigRxBuff(&can_pal1_instance, RX_MAILBOX, &buffCfg, 2);
CAN_SetRxFilter(&can_pal1_instance, CAN_MSG_ID_EXT, RX_MAILBOX, 0xFFFFFFFE);
The mailbox will receive the ID 0x2 and 0x3.
Also, the TX Mailbox and RX should be different.
If you want to check an example of how to do this check the .c attached. If you replace it in the can_pal example found in the SDK 3.0 should be enough to test it.
Let me know if this helps you
Best Regards,
Alexis Andalon