[support] integration with external mailing lists?

Hello, Does anyone know which external mailing lists integrate well [low effort] with Drupal? I'm looking for a mailing list system that my client(s) can use that provides nice tracking like: URL specific click-statistics for each news letter, reads per issue, unsubscribes per mailing... you know, all that good stuff that websites like: constant contact and list-rocket provide. I'm guessing that someone has already made a good connector to the user-profiles to one or more of these. Obviously one would want a check-box in Drupal's account admin pages to opt in/out of the mailing list(s). Thank you for your ideas and support! Best, Sebastian.