What information is held about email subscribers to a list?

The only information held about members is their email address, and (if you upload it or add it, or if they supply it) their first name and last name.

The interests.me system is not a complete membership management system - it only allows you to email your members or subscribers, not to take payment from them or manage their membership in any other way.

It's also worth noting that nobody within your team can see email addresses belonging to subscribers of a mailing list unless they have been granted access to that specific mailing list. So you can protect email addresses of subscribers from everyone except those who need access.