One thing to keep in mind is that if you say that your email address is at some throwaway email site, that throwaway email site has access to your email and can probably pretend to be you, can probably get control of your accounts elsewhere, as email is often used as a way to authenticate someone in the event of a forgotten password. That may not matter if you're just going to sign up and use a site once and then forget about it, but I'd be more-hesitant about using it for anything where you intend to use the thing on an ongoing basis or where there's anything sensitive associated with the thing.

Honestly, this would be a useful service for ISPs to offer. Like, temporary email addresses. Mine gives me a number of them, plus webmail access to them, but it's still a bounded number, not really intended to create one address for every possible remote location.

thinks

Abine.com used to provide proxy stuff for email addresses and credit card payments and SMS texts, hide your real identity from the other end, forward to your real one. They aren't free, though, or at least their credit card masking service isn't. I dunno if they're still in business.

checks

Yeah, though it looks like they now brand that service as "IronVest".

https://en.wikipedia.org/wiki/IronVest

https://ironvest.com/

Another issue is that a lot of websites that want to harvest email addresses block throwaway email domains, use services that can identify them.

It also creates problems for some places that don't care about harvesting email addresses, but do want to avoid bots, and try to block throwaway domains as well. For these, they make the assumption that an email address is an "expensive ID", something that one can't readily create a lot of. This is probably not a very good assumption, but, for example, a number of lemmy servers do this at sign-up. It'd be better to do something like a CAPTCHA or require a payment or something instead, IMHO...