I try to explain the problem.
If you set the monitor port in quad mode you can see all the BNC input in the same TV frame as follows:
BNC1 | BNC2
-------------
BNC3 | BNC4
and if motion occours, the mail is sent with the quad images perfectly.
If you set the monitor port in sequence mode you can see only one of BNC input at time in the TV frame as fiollows
-> BNC1->delay->BNC2->delay->BNC3->delay->BNC4 ->delay->
|< -- - - - - - - < - - - - - - - - < -- - - - - - - - < - - - - -|
If motion occours on BNC2 the mail is sent not with the BNC2 image but with the image currently displayed from monitor.
The image attached in the mail is the image present on monitor port when the motion occours!!