Thanks for the tutorial. I followed the steps last week and waited for the DNS to propagate but even four days later the mail settings were not showing up via a host example.com command. Then I saw this:
"Root domains with custom mail servers (MX records) must use A instead of CNAME records. Only your root domain (mydomain.com) may use A records. Non root domains (www.mydomain.com) must use the CNAME setup described above." from docs.heroku.com/custom-domains. So unless I am missing something the mail settings will not work until a A Record is added in thre GoDaddy DNS settings? I just set the A Record myself so I am now waiting to see if the mail will work now. Have you been able to use a mail server with the setup you described in the tutorial? Thanks!