It creates a content-aggregator site for your domain based on keywords important to your domain with a bunch of features related to building the traffic, monetizing etc.
But I digress. One of the features that I built was to allow users to send and receive emails using the domain names. This became an important feature once the site grows to become a bit more like a community (where users are submitting posts, comments etc) and there needs to be a way to engage with the userbase. It's also important for people who want to sell your domains.
The two specific features I built was
1) Using your existing GMail to send and receive emails with your custom domain 2) Forwarding your email to another inbox.
The email hardening advice given in this post is great - I've also added some of these and allow users to make changes to their DNS records directly.