Disposable email address
A disposable email address is a temporary address from a throwaway service that expires quickly and is not worth adding to a cold list.
Disposable addresses come from services that give anyone a short-lived inbox, often with no sign-up. People use them to avoid giving a real address. The inbox may be public, shared with others, or deleted after minutes or days.
They get into cold lists through sign-up forms, scraped data and old exports. Mailing them wastes volume. The messages are never read by a real prospect, the address may stop working, and the bounce raises your rate. Because the inbox can be public, other people can also read your message.
Remove them before you send. The services use many domains and new ones appear all the time, so a detector that checks a list of known domains is the practical way to catch most of them. It will not catch every case. Combine it with general verification, and ask where the addresses came from, because disposable addresses often point to a weak source.