Read domains from a CSV and get the IP of their MX.

mx.rb

# Read domains from a CSV and get the IP of their MX.
require 'resolv'
require 'csv'

Resolv::DNS.open do |dns|
  CSV.foreach('/Users/smith/Desktop/domains.csv') do |row|
    domain = row[1]
    next if domain == 'domain' # heading
    mxs = dns.getresources(domain, Resolv::DNS::Resource::IN::MX)
    if mxs.length == 0
      puts ""
    else
      begin
        puts dns.getaddress(mxs[0].exchange)
      rescue Resolv::ResolvError => e
        puts ""
      end
    end
  end
end