BuddyPress.org

i think is better use built-in function that queries the db to get user info.

Try with

function synchro_mailinglist($user_id, $password, $meta) {

$uid = get_userdata($user_id);

[…….]

$uid->user_email is the e-mail

It’s better use built-in functions because they are safer and they apply the filters and wp actions