Javax.mail.messagingexception: could not convert socket to tls

A Java Mail error!

The error message "Could not convert socket to TLS" typically occurs when the Java Mail API is trying to establish a secure connection (TLS) with a mail server, but the connection is not being established successfully.

Here are some possible causes and solutions:

1. Check the mail server configuration: Ensure that the mail server is configured to allow TLS connections. You can check the server's documentation or contact the server administrator to confirm.
2. Verify the TLS protocol version: Make sure that the Java Mail API is using a compatible TLS protocol version. You can try setting the mail.smtp.starttls.required property to false to disable TLS and see if the connection is established successfully.
3. Check the Java Mail API version: Ensure that you are using a compatible version of the Java Mail API. The TLS protocol has evolved over time, and older versions of the API may not support the latest TLS versions.
4. Check the Java version: Ensure that you are using a compatible version of Java. The TLS protocol has also evolved over time, and older versions of Java may not support the latest TLS versions.
5. Check the firewall settings: Ensure that the firewall settings are not blocking the connection to the mail server.
6. Check the mail server's certificate: Ensure that the mail server's certificate is valid and trusted by the Java Mail API. You can try setting the mail.smtp.ssl.trust property to true to trust all certificates.
7. Check the Java Mail API configuration: Ensure that the Java Mail API is configured correctly. You can try setting the mail.smtp.starttls.enable property to true to enable TLS.

Here is an example of how you can set these properties in your Java code:

Properties props = new Properties();
props.put("mail.smtp.starttls.required", "false");
props.put("mail.smtp.starttls.enable", "true");
props.put("mail.smtp.ssl.trust", "true");

Session session = Session.getInstance(props);

If none of these solutions work, you may want to try debugging the issue by enabling more verbose logging or using a tool like Wireshark to capture the network traffic and analyze the TLS handshake process.