How does Allah rewards such a person.?

There is no evidence that the individual is a Muslim and you also didn't post a link to his profile to prove your arguments. Hence claim is just invalid.

Hello and peace be upon you,

Its not clear whether the person who has written to you is a muslim or not.

However, this is an extremely hurtful and insulting email that he has written to you.

Muslims are told not to insult other religions.

Muslims are rather told to declare the oneness of one true God (without insulting their religion.)

Muslims are repeatedly told to treat others with kindness.

Did he just write this to you out of the blue? or were you guys already in an argument?

i think you should just put such messages in spam

he must be some unemployed person trying to instill some self worth in the name of some religion

i dont kw about allah and about reward systems

He is a coward as are you. But he's the bigger coward, i wouldnt call it bravery. So no reward.

A real man would meet face to face.

What? Are you a teen girl or something? We all receive hate mails

Something that doesn't exist can't DO anything.

In islam he would reward him by giving him your sister.