Is it possible to block all top level domains from sending mail? Like: ".in"

Meaning: We would block the servers: xxx.in yyy.in xxx.yyy.in .......just anything that ended in ".in"

I understand things can be faked and IP addresses are the better way to go, but we're getting a Ton of spam from ".in" and we don't regularly correspond with anyone using that top-level domain.

Thanks,
Joe