A disposable domain is a mailbox provider handing out throwaway addresses that stop being read minutes or hours after they are created. They exist to receive one confirmation link, and they are the single strongest signal in the email product.
What Spaw answers
disposable is true and the reason is disposable. The verdict is risky and the risk score carries +80, the largest weight on the email rate card.
A domain is matched two ways: by name against an open burner-domain list synced onto this server, and by the mail infrastructure behind its MX hosts, so a fresh vanity domain pointed at a known burner operator is caught even though its own name is on no list. Two override files in the repository settle the arguments — an allow list and a deny list, with allow winning.
The limits worth stating
The list is a list. A burner opened this morning under a new domain and its own MX is not on it, and a legitimate domain is sometimes listed by mistake; the check is a match against public data, not a judgement about the person typing. Spaw answers risky rather than undeliverable for exactly that reason — the mailbox usually does exist, it just will not exist for long.