Ask HN: Know of a Gmailish Interface for Self-Hosted Email?

Ok, let's change the context then. What if I run a web hosting company and want to offer an installable package that includes an MTA, MDA and a front end for viewing/sending mail? (I don't run a web hosting company, so I'm sure there are other things that need to go into that mix.) The customer would click a button and we would configure everything on their VPS or whatever. If that's not plausible enough, maybe I'm a web hosting company that just offers to host your email and now I've got enough scale to make it worth investing resources to ensure deliverability and spam filtering. At some point it's got to be worth running your own email infrastructure and for those scenarios, is there an installable front end that has the Gmail special sauce?

Thank you for the concrete suggestion! From the screenshots, Roundcube looks like a very good webmail client. It looks like they're going after Outlook though with their feature set and layout.

[Edit] But this is exactly what I'm looking for in terms of being an installable package that can be thrown on a web server and hooked up to an in-house or third party email infrastructure.

Roundcube is good and has come a long way over the years.