Good move! I was there before, and the worst part was... I was using a @gmail.com address. Bad mistake on my part. So actually tracking what I used the address with, that was my real pain. Now everything is on my custom domain, so if I need to move on from my current provider, it will be painless. In the process I did manage to delete a whole bunch of accounts I didn't use anymore.

Incidentally, I also moved to fastmail, and it is just boringly fantastic. It works. It has features I actually need and enjoy (masked emails!) and I recommend it to anyone who asks.