Can anyone please advise the best route or options to get mailing list type functionality for Drupal 6?

MailChimp seems by far to have the most traction, but I prefer not to be locked into a 3'rd party.

Mail handler with Mail Comment extension seems to have more traction than most, but there's something disconcerting about 35,000 downloads but only 2,600 active sites.

TIA