I suggest using mailchimp for mass-email. They track link clicks etc and also support templates so that you can send "Hello Jack, here's the beta link you asked

I suggest using mailchimp for mass-email. They track link clicks etc and also support templates so that you can send "Hello Jack, here's the beta link you asked about" to a many people at once. Make sure to enable google analytics integration as well. I didn't try personalized beta code, but more information is always better than less information.