How to block spam incoming email in plesk

Hi,

I've issue with spam email that spoof my domain and send it back to me.

e.g. On my domain server there is domain called a.com and i want to block any incoming email from a.com send to a.com from outside but not from internal (localhost).

So is it had function or method that allow me to block my domain email that sent from outside to internal.




Thanks for your help and upcoming solution.