Foreign IP Subnets

Is there a list of IP subnets that are assigned to networks in differnet countries or regions? I would like to block everything except US subnets from accessing my mail server. I have looked at RIPE, and the Asian counterpart for a list of subnets they control, and have not found anything compiled. I could do an ARIN search on every subnet I was concerned about to see where it is registered, but I think there is probably a better way. Thanks.
geo2020Asked:
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