Fast Mail DNS because I moved my domain over there for email. Problem is that it doesn’t have an API for DNS updates, and that makes it bad for DynDNS. There are some web scraping libraries out there that can work for it, but those can easily break any time FastMail changes their interface.

For now, I’m just using the fact that my IP doesn’t change that often, and living with the fact that I’ll have to manually update it at some point.