To quote another member who had the EXACT same issue I have:
- link to question
We have a multisite, multi-network buddypress install. When a new user is created or registered, they do not receive their activation email and end up in the "pending" section of the user list. Click to see the pending list and super admins are denied permission to access the page. The only place where we are able to create new users is in the network admin user list, not the site specific user list. This is also occurring with front end registration sign ups, they do not receive an activation email. This is happening across themes, so we believe it is a plugin conflict.
I didn't want to just hijack that Question, but it's not clear to me what the end solution was? Any help would be greatly appreciated.