This is not correct actually. An example of what's happening: A mask is created, let us say, on Yahoo. Yahoo says a verification code is sent to the mask's address but I do not receive it.

Can you see these emails as Blocked or Forwarded on relay.firefox.com ?

This support forum section you posted this thread in is for the Firefox Reality product https://labs.mozilla.org/projects/firefox-reality/

There is a form to use in getting Firefox Relay support as it is listed on https://support.mozilla.org/en-US/ and the form is https://support.mozilla.org/questions/new/relay/form