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.
Proton Mail has aliases that you can generate and then disable until you need it again. They are also integrated with simple login but I haven’t tried that out yet. I pay for unlimited so I have enough aliases (for now). I’ve even started creating ones specifically for my utilities like power, water, electricity, cable, etc.
I’ve just noticed Fastmail has a similar feature too