What is MailPoet?
It is an email plugin for WordPress, it allows you to quickly add content and images directly from your media library. There's no need to upload files to third-party services when you're all set, ready to go in your WordPress dashboard.
What is MailPoet with BuddyForms?
It is a combination that allows MailPoet techniques to be used in conjunction with BuddyForms forms and for users to register in lists more easily.