Does anyone know of a neat system to put people into mailing lists where the system does a two way sync between PD and the email marketing program.

For example, I put a custom field against people called 'mailing list' and give options of mailing list A and mailing list B. I set a person to mailing list A and they get added to that list in the emailing marketing program and if I change them to B, it then moves them over to B in the email marketing program.

I know that mailchimp syncs with PD but it only appears to be a minimal sync and not quite as good as the above.

What system and setup do you guys use?