SMTP Handshake
The process of connecting to a mail server to verify if a specific mailbox exists, without actually sending an email.
An SMTP handshake is a conversation between two mail servers following the Simple Mail Transfer Protocol. During email verification, this handshake is used to check if a mailbox exists without actually delivering a message.
The verification handshake process: 1. EHLO/HELO: The verifier identifies itself to the mail server 2. MAIL FROM: Specifies a sender address 3. RCPT TO: Specifies the email address being verified 4. The server responds with a status code: - 250: Mailbox exists (valid) - 550: Mailbox doesn't exist (invalid) - 452: Mailbox full or temporarily unavailable - 250 (catch-all): Server accepts all addresses
Limitations:
- Some servers don't respond honestly (catch-all domains)
- Rate limiting can block verification attempts
- Greylisting can delay responses
- Some servers block verification-pattern connections
SendSure's 27-stage engine goes far beyond basic SMTP handshakes, using DNS analysis, disposable detection, AI scoring, and external signal sources for comprehensive verification.
Related Terms
Email Verification
The process of confirming whether an email address is valid, deliverable, and belongs to a real person.
Catch-All (Accept-All)
A domain configured to accept emails sent to any address, regardless of whether the specific mailbox exists.
Greylisting
A spam prevention technique where a mail server temporarily rejects emails from unknown senders, expecting legitimate servers to retry.
Related Blog Posts
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