[@robin-w Moderator 13 years ago]

it uses the wordpress user database to store email addresses, and will mail to the email address of the wordpress user as you set them up.

Whilst a bit clunky, you could use

https://wordpress.org/plugins/export-users-to-csv/

to export the email addresses to a csv, and import them from there to mailchimp maybe via a macro.

depends on how many users you have and how often you’re emailing.