They work by giving you a random email address that is available for a short time (ex. 10min) and an inbox for any messages you recieve during that time (ex. an email verification message from a Lemmy server)
I didn’t want to recommend a specific one, however Googling “temporary email” should give you several options to choose from.
For me it didn’t need email to sign up, most likely wouldn’t have if it did. In any case a temp email defeats the purpose of a recovery email.