Why a PC?
My Pi2 based server has been up and running for several months now. I first started looking at doing this because I found that, believe it or not, my large UK based domain and email provider was treating M&S order acknowledgements as spam, despite my email service being supposedly configured to accept all spam so I could sort it out on my clients.
So I bought a Pi2, added a little inbuilt UPS module which is probably unnecessary but there to handle shut down tidily, and built an email server. The links include all the information necessary to get to a domain provider who handles non static IPs for you:
This chap, Sam Hobbs, is not me: