Paul Howarth <paul(_at_)city-fan(_dot_)org> writes:
Unfortunately the output of whois servers is well-nigh impossible to
parse in a reliable, automated and useful fashion due to the enormous
variation in data formats of the various registries. Hence whois data
is wholly unsuitable for playing any part in the decision whether or
not to accept a given mail item when it arrives.
Plus also, some whois servers do not allow multiple queries from a
single source and will blacklist you if you attempt to look up too
many domains in a given period. This also makes it unacceptable to
use whois as part of the decision whether or not to accept email.