random_data gem was failing to generate unique emails (after ~ 7000 loops), so I decided to add a random number. It passed the test even with 1M loops!

random_utils.rb

require 'rubygems'
require 'random_data'
require 'spec'

describe "random data" do
  it "should be unique" do
    prev = RandomUtils.random_email

    (1..100000).each do |n|
      email = RandomUtils.random_email
      puts email
      puts "*** #{n} ***"

      email.should_not == prev
    end
  end
end

class RandomUtils
  def self.random_number
    rand(100000000 + rand(10000 + rand(10000)))
  end

  def self.random_email
    "#{random_number}#{Random.email}"
  end
end