Back in February we wrote about Facebook’s secret Project Titan—a web-based email client that we hear is unofficially referred to internally as its “Gmail killer”. This isn’t a big surprise—the event invites Facebook sent out hinted strongly that the news would have something to do with its Inbox, sparking plenty of speculation that the event could be related to Titan. Our understanding is that this is more than just a UI refresh for Facebook’s existing messaging service with POP access tacked on. Rather, Facebook is building a full-fledged webmail client, and while it may only be in early stages come its launch Monday, there’s a huge amount of potential here.