I got Mailpile running on a $5/mo droplet a day or two ago, but I'm getting out-of-memory errors , and "Too many files open" exceptions from python. I haven't looked too closely at it yet, but I suspect it's the indexer in Mailpile trying to index the ~70,000 messages I have. In any case, despite these errors, it works pretty well, though indexing my messages is slooooooooow. I'm running Debian Wheezy, so I can't particularly comment on running it on Ubuntu 14.04. To get it running, I pretty much just git-cloned the source, made sure that I had all the dependencies installed (found in requirements.txt), and then ran the script ./mp. I could be wrong, but I think Mailpile is written for python2.7. I don't know if it works on python3.3 yet, which I think is the default python version in Ubuntu 14.04. If you're having problems getting it going on 14.04, then perhaps the python version would a good place to start looking.

I haven't had the chance to play with it myself. The interface looks great and built in PGP integration is definitely something I want to check out. So I'l love to hear feedback from anyone using it too!

One thing to note, is that right now it is simply a front end. From their download page:

Mailpile is not an email server (MTA). Services like Gmail, Yahoo, and others provide both the email "client" and "server" in one package. However, you can use Mailpile with your Gmail to be more secure!

At some point in the future, we would love to offer better tools and integrations for Mailpile that make the email server component easier to integrate with. But, doing this the right way that doesn't compromise security or ethics takes time to create. Until that point in the future, if you're handy with the command line, you might want to consider setting up a mail server using one of the following open source projects. Each options has the goal of making self hosting an email server much easier.

The claim that it can make "your Gmail to be more secure." Seems a little off to me. Unless you are encrypting every message, they are still being store on Google's servers. So YMMV.