emails = []
emails = File.readlines('Customers.csv').to_a.map{|line| line.split(/;/)[11].chomp}.select{|e| !e.empty?}

dup_list = []

while email = emails.shift
  flag = false
  emails.each do |email2|
    if email == email2
      dup_list << email 
      break
    end
  end
  if flag
    emails.delete(email)
  end
end
require 'pp'
pp dup_list