You probably came to this page because I told you to send email to <something>@secretinbox.net and you're confused about if that's a real thing.
It is, and I will get your mail if you send it. This domain allows me to use relaxed spam filtering as compared to my primary public addresses, as each sender should have their own address and if they leak the address in such a way that causes spam it can simply be disabled. You should get used to the idea of people giving you bespoke addresses with services like "Hide My Email" by Apple or Duck Duck Go's email protection service.
If your mail is being rejected, then please reach out to me using the information in the rejection message or through alternative contact information that you should have through our relationship.