Why am I getting TLS errors when sending to Gmail?

Email marketer from Reddit shares possible reasons for a GSuite SMTP 421 error, including Google rate limiting accounts for sending too much email, Google detecting possible SPAM (so is limiting accounts), or the user needs to authenticate with Google

Email marketer from MXToolbox shares that using the MXToolbox SMTP Test tool can help diagnose TLS connection issues by testing if the server supports STARTTLS and what TLS versions are available.

Email marketer from DigitalOcean shares that If using Let's Encrypt, ensure the certificate is automatically renewed to prevent expiration. Errors can arise if the renewal process fails.

Email marketer from StackOverflow shares that TLS handshake failures can occur if the client and server don't support a common TLS protocol version or cipher suite. Also firewall or network issues can interrupt the TLS handshake.

Email marketer from cPanel Forum explains that TLS errors can occur if the SSL certificate is not correctly installed or has expired. Ensure the certificate is valid, properly installed for the SMTP service, and trusted by the receiving server.

Email marketer from Reddit responds by suggesting checking the email server's TLS configuration and ensuring it supports the required TLS version. They also mention it could be a temporary issue on Gmail's side.

Email marketer from StackExchange responds by suggesting that issues with SSL/TLS could stem from outdated SSL libraries or configurations on the server, particularly if the server's cipher suites are not compatible with Gmail's requirements. Update SSL libraries, review supported cipher suites, and confirm your SSL certificate is correctly installed.

Email marketer from EasyDMARC shares that ensuring proper authentication configurations with SPF, DKIM, and DMARC can reduce TLS errors. Proper authentication allows sending servers to be validated, which can improve the connection.

Email marketer from SuperUser suggests verifying that the SMTP server is configured to use STARTTLS. They also suggest checking the mail server logs for specific error messages.

Email marketer from AuthSMTP shares that often the issue is the SSL/TLS certificates that you or your recipient are using are not trusted, either because they are self-signed, or signed by an untrusted Certificate Authority. Your mail client or server must trust the Certificate Authority that signed the SSL/TLS certificate for the connection to work

Expert from Email Geeks explains the need to configure or fix TLS on outbound emails, suggesting the use of aboutmy.email to diagnose the issue.

Expert from Email Geeks suggests that Google thinks STARTTLS is not being used and recommends analyzing logs for systemic issues if throttling is frequent.

Expert from Word to the Wise shares that TLS errors can occur if the email server is not configured to use TLS, the TLS certificate has expired, or the TLS version is not supported by the recipient's server. It is important to ensure that TLS is enabled, that the TLS certificate is valid, and that the TLS version is supported by both sender and receiver. The TLS configuration can be checked using online tools such as SSL Checker or by inspecting mail server logs.

Expert from Email Geeks recommends using aboutmy.email to examine TLS setup details for better advice, downplaying the likelihood of a Gmail error.

Expert from Email Geeks suggests checking the TLS setup to ensure it's working correctly, indicating a possible issue on the sender's side rather than Gmail's.

Expert from SpamResource shares that TLS errors arise due to certificate issues, mismatched protocols, or problems negotiating encryption. Start by verifying your SSL/TLS configuration, ensuring the certificate is valid and properly installed, and checking for compatibility issues with Gmail's required protocols. If problems persist, check if recent software changes might have affected encryption and run diagnostics to verify TLS support.

Expert from Email Geeks says that Gmail may have started enforcing TLS, or it could be related to volume or reputation and indicates that the certificate might have expired.

Documentation from Google Workspace Admin Help explains that Gmail requires all bulk email senders to use TLS/SSL for SMTP connections. The error `421-4.7.29` indicates that the message wasn't sent over a TLS connection.

Documentation from RFC Editor specifies that STARTTLS allows SMTP servers to negotiate TLS encryption after establishing a plain text connection. It's important that both the client and server support this extension.

Documentation from OpenSSL explains that TLS errors often arise from configuration mismatches, certificate problems, or protocol incompatibilities. The documentation recommends using s_client to test the connection and diagnose the specific issue.