How to force JavaMailSenderImpl to use TLS1.2?

This is the fix for the next guy looking:

mail.smtp.starttls.enable=true;
mail.smtp.ssl.protocols=TLSv1.2;

It didn't work for me in one pretty old app and I couldn't realize why. After some research I found that the javax.mail version in the app dependencies was 1.4. You must upgrade to at least 1.5.

I needed both Vojtech Zavrel and Sunny's answer in my case. I was running Java 1.8 Spring Boot 1.2.5 and running on Big Sur 11.2.3 and spring version 4.2.1.RELEASE.

After I updated my dependency like this

<dependency>
        <groupId>javax.mail</groupId>
        <artifactId>mail</artifactId>
        <version>1.5.0-b01</version>
</dependency>

and I updated my JavaMailSenderImpl with

Properties prop = new Properties();
prop.setProperty("mail.smtp.auth", "true");
prop.setProperty("mail.smtp.starttls.enable", "true");
prop.setProperty("mail.smtp.ssl.protocols", "TLSv1.2"); // Added this line
prop.setProperty("mail.smtp.ssl.trust", mailUri.getHost());
mailSender.setJavaMailProperties(prop);

I saw the Received fatal alert: protocol_version error resolve.

An update to the most recent version (1.6.2.) of Java Mail also fixes the issue. In my case I upgraded from:

<dependency>
    <groupId>javax.mail</groupId>
    <artifactId>mail</artifactId>
    <version>1.5.0-b01</version>
</dependency>

to:

<dependency>
    <groupId>com.sun.mail</groupId>
    <artifactId>javax.mail</artifactId>
    <version>1.6.2</version>
</dependency>

This fixed the error

javax.mail.AuthenticationFailedException: 421 4.7.66 TLS 1.0 and 1.1 are not supported. Please upgrade/update your client to support TLS 1.2

I was getting from an Outlook SMTP-Server. No property changes needed.