require 'resolv'
def valid_email_host?(email)
hostname = email[(email =~ /@/)+1..email.length]
valid = true
begin
Resolv::DNS.new.getresource(hostname, Resolv::DNS::Resource::IN::MX)
rescue Resolv::ResolvError
valid = false
end
return valid
end
valid_email_host?('j@l.m') # => false
valid_email_host?('joe@oreilly.com') # => true