S2Member is highlighting the following warning and by elimination it's Postie that is triggering the conflict. Is there any workaround?
"New User Email Configuration:-
Conflict warning: You have another theme or plugin installed that is preventing s2Member from controlling this aspect of your installation. When the pluggable function wp_new_user_notification() is handled by another plugin, it's not possible for s2Member to allow customization of New User Emails".