My dynamic IPv6 prefix hasn’t changed in a couple of years. It only changed because I reset the router config and that changed my DUID. That’s good enough for everything I host. I don’t even bother with dynamic DNS anymore.

I wouldn’t bother with trying to host an email server from a residential connection though. Even if you can get your ISP to open port 25 for you, many email servers won’t accept mail from residential IP addresses.