Comment by calvins

There is spamgourmet (https://www.spamgourmet.com/index.pl). It doesn't satisfy 4 exactly, but it's pretty close. If you give out an email like '[email protected]' (there are other domains too), then it'll forward 20 emails to the configured email for your account, but you can always log in and set it to 0 remaining at any point, regardless of how many emails have been received.