Shameless plug here, but that is the purpose of [ImprovMX](https://improvmx.com). We forward emails from a custom domain to a destination email that can be updated.

My personal email is contact@{custom domain} and currently points to Gmail because I never took the hassle to change it, but if someday I decide to move elsewhere (I'm contemplating Fastmail and Protonmail), all I will have to do is update my destination email at ImprovMX and that's all.

This is a liberty that only us, tech people, can grasp. My parents, even my wife, doesn't see the importance of being locked to mail provider.