There have been a lot of remailers in the past. It's hard for me to see what legitimate purpose this service provides for Mozilla as an organization or for users of the free web. It would be nice to have an account-specific email address that is not shared with other services. (We kinda have that with the "+" trick.) But it can't process replies so that dramatically limits the use-cases for non-spammers.
what happens when most services of interest promptly block @relay.firefox.com addresses?
Just like they do with 10minutemail addresses and such.
This service is dead on the water.
https://temp-mail.org/ Switches and adds new domains regularly. That's necessary for such a service like this.
But even worse, what happens when Mozilla decides to pull the plug after a year (like they do with 80% of their projects)?
Couldn't this be used to make a large number of "free trial" emails, for say, Netflix or Amazon Prime?
Email is the least resistance, it doesn't matter. It doesn't provide the cards required to start the trial (prepaids not allowed)