I can use my own domain for free and it works just fine with IPv4 and IPv6.
I'm using it with am apple airport router and it's working fine
No-IP - Dynamic DNS and Managed DNS Provider
dmarcian - Safeguard your email from abuse
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Proofpoint - Proofpoint provides cloud-based email security, e-discovery and compliance solutions for companies to protect sensitive business data.
iWantMyName - Register your own custom domain for web applications, email, blog or website such as Google Apps...
Hornetsecurity - Hornetsecurity offers you comprehensive, integrated managed e-mail security services.