Ajit,
In the industry solution mill products there is specific functionality to do CO-Product good receipt posting during CO11N (and other confirmation transactions). By-products are not supported in this scenario.
It is way more common in the mill industries to use co-products rather than by-products. This is a good explanation about the difference between co- and by-products: Co product and By Product
A by-product can be automatically posted during confirmation when you use the backflash functionality.
Regards
Stefan