If you need email, but also web/ftp/git/mysql/dns, try Virtualmin - http://www.webmin.com/virtualmin.html - you can easily run this on a $5 digital ocean server.
You basically follow a web installation wizard, create a domain and then you can use Roundcube (included) or any IMAP client. Couldn't be easier.
A +1 for Virtualmin. Does all that th OP's server does (I think) plus can do it for multiple domains and has a simple web ui. Free, and their support forum is helpful.
You basically follow a web installation wizard, create a domain and then you can use Roundcube (included) or any IMAP client. Couldn't be easier.