e.g.
apt-get install gmail-server
e.g.
apt-get install gmail-server
Still, shouldn't be that hard to do as long as it is your own server and you trust it; I imagine a lot of the difficulty of gmail is scaling, and even a single user with 20-50GB of mail isn't in the same league.
If you were to outsource it to a service provider:
I'd love a way to do privacy-protecting search on my mailbox, either by building/maintaining a local index, or even more amazingly, some kind of cryptographic/data structure magic: do processing once either pre-encryption or on the local device, then add it to an index, with a configurable slider for data leakage vs. search quality. Search could execute locally and remotely.
(This is to allow you to use webmail with no local persistent storage, or a new phone, to search your email on a server, without trusting the server).
I download my email to the Mac mail app. That has let me find some emails that were unfindable on the web interface (even when I searched by sender email!)
Mutt is more like "everything I can come up with from the command line." Sure, I won't make my grandma use it, but I've never needed any searching capability beyond grep and co.
Still, I do think there exist some very talented grafic designers out there that would enjoy playing around with a webmail interface. Hopefully, articles like this will increase the demand and interest in run-it-your-self webmail packages, so one would do that and not spend all focus on building more CMSes.