Privacy
Firefox Relay
Try a website without giving it your main email
Browser5 free email masks · premium extras paid
Open Firefox Relay Why this one
Give a newsletter or a low-stakes signup a forwarding address instead of your main email. If that address attracts unwanted mail, you can block its forwarding.
Try this first
Sign in with a Mozilla account, create one email mask and use it for a nonessential newsletter. Check that its confirmation reaches your real inbox.