What are SSL/TLS handshake failures?
SSL/TLS handshake failures prevent secure connections:
What the handshake does:
Establishes encrypted connection. Verifies server identity via certificate. Negotiates encryption parameters. Enables STARTTLS upgrade.
Failure causes:
Certificate expired: Server certificate past validity date. Certificate mismatch: Certificate does not match hostname. Protocol incompatibility: TLS version not supported. Cipher suite mismatch: No common encryption algorithms.
Email impact:
Connection may fall back to unencrypted (if allowed). Strict TLS policies cause delivery failure. 454 or similar codes returned.
Resolution:
Check certificate validity and hostname. Verify TLS configuration. May be receiving server's problem. May need to allow fallback for specific domains.
Handshake failure is a botched secret greeting. The encrypted channel cannot be established.
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