Not to be overly negative, but if you're going to the trouble of pointing a custom domain to this service, couldn't you just write a quick PHP script that mail(

Not to be overly negative, but if you're going to the trouble of pointing a custom domain to this service, couldn't you just write a quick PHP script that mail()s out when it's accessed? As far as I can see, the only advantage of using this third-party site is convenience, a custom domain makes it much less so.