How to verify the TLS version used in javax.mail.*;

Question

When connecting to an SMTP server using javax.mail , how can I make sure that the version of TLS is v1.2 or higher.

I am using Java version 8 (update 162).

Answer 1

To ensure the TLS version used:

props.put("mail.smtp.ssl.protocols", "TLSv1.2");

I don't have the means to 100% confirm that I am connecting with v1.2 but this is what I found. How to force JavaMailSenderImpl to use TLS1.2?

Answer 2

You can use the following snippet to get a space delimited list of the supported protocols:

String.join(" ", SSLContext.getDefault().getSupportedSSLParameters().getProtocols());

In Java 8 that would return a list with TLSv1.2 as the highest version and a list with TLSv1.3 as the highest version in Java 11.

Then simply set the System property mail.smtp.ssl.protocols to that value, e.g.

String protocols = String.join(" ", 
    SSLContext
        .getDefault()
        .getSupportedSSLParameters()
        .getProtocols()
);

System.setProperty("mail.smtp.ssl.protocols", protocols);