Just in case you happen to be a 1Password user as well, there is an integration where they can auto-generate masked emails for you: https://support.1password.com/fastmail/ It makes it very convenient!

Auto-generated masked emails using Fastmail and 1Password has worked very well for me when I'm using Firefox, with the 1Password extension installed, on my laptop.

I can't for the life of me, however, figure out how to get 1Password to auto-gen a masked email from their iPhone app or desktop app.

Is this possible?

Would love to see a Bitwarden implementation of this

You can also use a custom domain (and/or anything else Fastmail lets you choose), this way you can put all the randomly generated emails coming to you in a single folder (as a rule).