This gives you the benefit of disable-able email addresses, but not the benefit of privacy. Those companies (and once leaked, anyone) can use your custom email domain as a fingerprint for your online activity.

(Source, I'm the creator of Owl Mail [https://owlmail.io] and this is a common question.)

Interesting. Curious: how is that any different than if owlmail gets leaked?

If you give your personal email address to hundreds of services online one of them is bound to sell or leak your email.

By using Owl Mail (or Firefox Relay, etc.) addresses everywhere, you reduce your attack surface to one security fastidious company.

And, even if Owl Mail (or Firefox Relay, etc.) were to experience a data breach, at least it would greatly increase the effort required to match emails to your identity.

To really protect yourself, use a double relay!

  External -> Relay 1 -> Relay 2 -> Your Inbox

Then you will have some serious resilience :D

Oo, I like that! Really good point there.

Also, I think one thing you should look into as a natural evolution is promoting the use of auto-generated, secure passwords unique to each relay address.

How is Owl Mail funded?

There will be paid plans.