Learn how to troubleshoot “Sendmail Verify=Fail” errors in Maillogs. Our Sendmail Support team is here to help you with your questions and concerns.

Troubleshoot “Sendmail Verify=Fail” Errors in Maillogs

Have you come across encounter entries in the maillog file like this”

sendmail[28450]: STARTTLS=client, relay=mail.example.com.netsolmail.net., version=TLSv1/SSLv3, verify=FAIL, cipher=DHE-RSA-AES256-SHA, bits=256/256

According to our Experts, this error indicates that Sendmail failed to verify the SSL/TLS certificate of the remote mail server during the SMTP handshake. This issue occurs when Sendmail cannot confirm the authenticity of the remote server’s certificate, potentially affecting the security of the email connection.

Why Does “Sendmail Verify=Fail” Happen?

Sendmail performs certificate verification as part of its security measures during the SMTP handshake. This process ensures secure communication between mail servers by validating the authenticity of the remote server. When verification fails, the issue typically lies in one or more of the following areas:

• The remote server’s SSL/TLS certificate may be expired, invalid, or misconfigured.
• The issuing CA of the remote server’s certificate is not recognized by your server’s CA bundle, possibly due to missing root or intermediate certificates.
• Problems like DNS resolution failures, blocked ports, or firewall restrictions can disrupt the verification process.
• Misconfigured TLS settings or an outdated CA certificate bundle on your Sendmail server can prevent successful verification.

Impacts of “Verify=Fail”

While this error does not always block email delivery, it can affect the security of the mail system:

• Without certificate verification, the connection may be vulnerable to spoofing or man-in-the-middle attacks.
• Failure to maintain secure email transmissions could lead to non-compliance with industry standards or policies.

Troubleshooting Steps

• Use tools like `openssl s_client` to analyze the remote server’s certificate:

  openssl s_client -connect mail.example.com:25 -starttls smtp

  Look for expiration dates, validity, or missing intermediate certificates.
• Ensure the Sendmail server uses the latest CA bundle:

  On Linux, update CA certificates using your package manager:

  sudo update-ca-certificates
• Verify DNS resolution and check for firewall rules that may block SMTP connections:

  dig mail.example.com
telnet mail.example.com 25

• Also, check `sendmail.mc` and ensure proper TLS settings. Rebuild the configuration if necessary:

  define(`confCACERT_PATH', `/etc/pki/tls/certs')dnl
define(`confCACERT', `/etc/pki/tls/certs/ca-bundle.crt')dnl
define(`confSERVER_CERT', `/etc/pki/tls/certs/sendmail.pem')dnl
define(`confSERVER_KEY', `/etc/pki/tls/private/sendmail.key')dnl

• Review Sendmail logs for detailed error messages and the remote server’s logs if you have access.

Additional Considerations

• Implement SPF, DKIM, and DMARC to strengthen your email security alongside TLS.
• Occasionally, “verify=fail” may be due to temporary network glitches or specific server configurations.
• If verification failures disrupt critical email delivery, consider relaxing TLS requirements temporarily, but weigh this carefully against potential security risks.

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Conclusion

The “sendmail verify=fail” error is a crucial indicator of SSL/TLS certificate verification issues during SMTP handshakes. While it does not always block email delivery, addressing it promptly helps ensure secure and reliable email communication.

In brief, our Support Experts demonstrated how to fix “Sendmail Verify=Fail” errors in Maillogs.