I use S2Member and it has the capability of customizing the new member email confirmation. However, it appears that NextGen conflicts. I get this message in S2Member:
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. This is NOT a major issue. In fact, in some cases, it might be desirable. That being said, if you DO want to use s2Member’s customization of New User Emails, you will need to deactivate one plugin at a time until this conflict warning goes away.
This is a link to the S2Member support site that may point to the problem:
https://www.s2member.com/forums/topic/strange-conflict-with-plugin/
Any help would be appreciated. Thank you.