SMTP
The protocol for sending email, also used to verify an address by dialoguing with the receiving server.
SMTP (Simple Mail Transfer Protocol) governs how email moves between servers. Email verification uses it without sending a message: it opens a conversation with the recipient server and asks whether a given address would be accepted.
The server's answer (accept, reject, catch-all) lets you classify the address. Some servers block this kind of probe, which is why SMTP must be combined with other validation methods.
Related terms
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