Why is STARTTLS negotiation failing with the error 'connection died while negotiating STARTTLS TLS'?
Summary
What email marketers say10Marketer opinions
Email marketer from ServerFault mentions that an outdated OpenSSL library on the sending server can cause STARTTLS failures, especially when communicating with servers using newer TLS protocols. Updating OpenSSL may resolve the issue.
Email marketer from Email Admins Group shares that if the receiving server requires a specific authentication mechanism after STARTTLS, and the sending server doesn't support it or isn't configured correctly, the connection can die during negotiation. Ensuring authentication methods are compatible is key.
Email marketer from Reddit explains that issues can happen when there are differences between the TLS versions or cipher suites available on your server and what the receiving server is willing to accept. Try matching these up.
Email marketer from Linux Forums suggests that the error might be due to resource exhaustion on the server, such as high CPU usage or insufficient memory. Monitoring server resources and optimizing performance could resolve the issue.
Email marketer from Stack Overflow shares that this error can happen when the client attempts STARTTLS but the server either doesn't support it or has it disabled. It recommends checking if the server advertises STARTTLS in its EHLO response and ensuring the client is configured to handle the server's capabilities.
Email marketer from Super User suggests that the error can occur if the sending server's hostname does not match the hostname in its SSL certificate. This mismatch can cause the receiving server to terminate the TLS negotiation. Ensure these match.
Email marketer from Email Marketing Forum points out that temporary network glitches or intermittent DNS resolution issues can sometimes cause this error. Restarting the mail server or checking DNS settings may help.
Email marketer from Security Blog explains that overly aggressive security settings or intrusion detection systems (IDS) can interfere with the STARTTLS handshake. The recommendation is to review security logs and adjust IDS rules to allow the TLS negotiation.
Email marketer from SSL Support Forum indicates that an expired or improperly configured intermediate certificate can cause STARTTLS failures. Ensuring the correct chain of trust is established can fix the issue.
Marketer from Email Geeks suggests the TLS engine is too strict with matching cert CNs.
What the experts say5Expert opinions
Expert from Word to the Wise explains that one potential cause of STARTTLS negotiation failures is a problem with the SSL/TLS certificate, such as an expired certificate or a mismatch between the hostname and the certificate's subject name. The fix may involve renewing the certificate, ensuring correct hostname configuration, or checking certificate chain issues.
Expert from Email Geeks suggests the issue might be that the sender is negotiating with a key the recipient doesn’t like.
Expert from Email Geeks suggests testing the connection manually using SWAKS to get a clearer error message regarding the STARTTLS negotiation failure.
Expert from Email Geeks clarifies that manually connecting means using SWAKS for TLS connections.
Expert from Email Geeks shares results of a successful TLS negotiation with the recipient domain, suggesting that the sender's TLS system might be faulty or incompatible.
What the documentation says5Technical articles
Documentation from OpenSSL.org notes that specific OpenSSL versions have known issues related to TLS negotiation with certain cipher suites or protocol versions. The documentation suggests checking the OpenSSL version and updating it if necessary.
Documentation from cPanel Documentation suggests the problem may be related to an incorrect SSL configuration on the server, or a mismatch in supported ciphers. It recommends ensuring that the server's SSL certificate is valid and that the cipher suites are compatible between the client and server.
Documentation from RFC Editor (RFC 3207) details that the STARTTLS extension allows the encryption of SMTP sessions. If a client and server do not properly implement this extension, negotiation can fail.
Documentation from Microsoft Learn explains that this error often indicates a network issue or firewall blocking the STARTTLS handshake on port 25. It advises checking firewall rules and network connectivity between the sending and receiving servers.
Documentation from Postfix.org indicates that a common cause is a misconfiguration in the Postfix TLS settings. The documentation advises verifying the `smtp_tls_security_level` and related parameters in the Postfix configuration to ensure they are correctly set for opportunistic or mandatory TLS.