<bean id="mailSender" class ="org.springframework.mail.javamail.JavaMailSenderImpl" >
    <property name="username" value="XXX@gmail.com" />
    <property name="password" value="XXX" />
    <property name="javaMailProperties">
    <props>
        <prop key="mail.smtp.host">smtp.gmail.com</prop>
        <prop key="mail.smtp.port">587</prop>
        <prop key="mail.smtp.auth">true</prop>
        <prop key="mail.smtp.starttls.enable">true</prop>
    </props>
    </property>
</bean>

<bean id="mailSender" class ="org.springframework.mail.javamail.JavaMailSenderImpl" >
    <property name="username" value="XXX@gmail.com" />
    <property name="password" value="XXX" />
    <property name="javaMailProperties">
    <props>
        <prop key="mail.smtp.from">XXX@gmail.com</prop>
        <prop key="mail.smtp.user">XXX@gmail.com</prop>
        <prop key="mail.smtp.password">XXX</prop>
        <prop key="mail.smtp.host">smtp.gmail.com</prop>
        <prop key="mail.smtp.port">587</prop>
        <prop key="mail.smtp.auth">true</prop>
        <prop key="mail.smtp.starttls.enable">true</prop>
    </props>
    </property>
</bean>

<property name="host"><value>smtp.gmail.com</value></property>
        <property name="port"><value>587</value></property>
        <property name="protocol"><value>smtp</value></property>
        <property name="username"><value>${mail.username}</value></property>
        <property name="password"><value>${mail.password}</value></property>
        <property name="javaMailProperties">
            <props>
                <prop key="mail.smtp.auth">true</prop>
                <prop key="mail.smtp.starttls.enable">true</prop>
                <prop key="mail.smtp.quitwait">false</prop>
            </props>
        </property>

mail.protocol=smtp
mail.host=smtp.gmail.com
mail.port=465
mail.smtp.socketFactory.port=465
mail.smtp.auth=true
mail.smtp.starttls.enable=true
mail.smtp.debug=true
mail.smtp.starttls.required=true
mail.smtp.socketFactory.fallback=false
mail.from=XXX@gmail.com
mail.username=XXX@gmail.com
mail.password=my_password

@Configuration
@PropertySource("classpath:mail.properties")
public class MailConfiguration {

    @Value("${mail.protocol}")
    private String protocol;
    @Value("${mail.host}")
    private String host;
    @Value("${mail.port}")
    private int port;
    @Value("${mail.smtp.socketFactory.port}")
    private int socketPort;
    @Value("${mail.smtp.auth}")
    private boolean auth;
    @Value("${mail.smtp.starttls.enable}")
    private boolean starttls;
    @Value("${mail.smtp.starttls.required}")
    private boolean startlls_required;
    @Value("${mail.smtp.debug}")
    private boolean debug;
    @Value("${mail.smtp.socketFactory.fallback}")
    private boolean fallback;
    @Value("${mail.from}")
    private String from;
    @Value("${mail.username}")
    private String username;
    @Value("${mail.password}")
    private String password;

    @Bean
    public JavaMailSender javaMailSender() {
        JavaMailSenderImpl mailSender = new JavaMailSenderImpl();

        Properties mailProperties = new Properties();
        mailProperties.put("mail.smtp.auth", auth);
        mailProperties.put("mail.smtp.starttls.enable", starttls);
        mailProperties.put("mail.smtp.starttls.required", startlls_required);
        mailProperties.put("mail.smtp.socketFactory.port", socketPort);
        mailProperties.put("mail.smtp.debug", debug);
        mailProperties.put("mail.smtp.socketFactory.class", "javax.net.ssl.SSLSocketFactory");
        mailProperties.put("mail.smtp.socketFactory.fallback", fallback);

        mailSender.setJavaMailProperties(mailProperties);
        mailSender.setHost(host);
        mailSender.setPort(port);
        mailSender.setProtocol(protocol);
        mailSender.setUsername(username);
        mailSender.setPassword(password);
        return mailSender;
    }
}

<beans>
    <bean id="mailSender" class="org.springframework.mail.javamail.JavaMailSenderImpl">
        <property name="host"><value>smtp.gmail.com</value></property>
        <property name="port"><value>465</value></property>
        <property name="protocol"><value>smtp</value></property>
        <property name="username"><value>XXXXX@gmail.com</value></property>
        <property name="password"><value>XXXX</value></property>
        <property name="javaMailProperties">
            <props>
                <prop key="mail.smtp.auth">true</prop>
                <prop key="mail.smtp.starttls.enable">false</prop>
                <prop key="mail.smtp.quitwait">false</prop>
                <prop key="mail.smtp.socketFactory.class">javax.net.ssl.SSLSocketFactory</prop>
                <prop key="mail.smtp.socketFactory.fallback">false</prop>
                <prop key="mail.debug">true</prop>
            </props>
        </property>
    </bean>
    <bean id="mailMail" class="com.embitel.service.email.EmailService">
        <property name="mailSender" ref="mailSender" />
        <property name="simpleMailMessage" ref="customeMailMessage" />
    </bean>
    <bean id="customeMailMessage" class="org.springframework.mail.SimpleMailMessage">
        <property name="from" value="XXXX@gmail.com" />
        <property name="to" value="yyyyy@gmail.com" />
        <property name="subject" value="Testing Subject Line for email senind.." />
        <property name="text">
            <value>
        <![CDATA[
            Dear %s,
            Mail Content : %s
        ]]>
            </value>
        </property>
    </bean>
</beans>

<prop key="mail.smtp.starttls.enable">true</prop>

public JavaMailSender getJavaMailSender()
    {
        JavaMailSenderImpl sender = new JavaMailSenderImpl();
        sender.setProtocol("smtp");
        sender.setHost("smtp.gmail.com");
        sender.setPort(587);
        sender.setUsername("username");
        sender.setPassword("password");

        Properties mailProps = new Properties();
        mailProps.put("mail.smtps.auth", "true");
        mailProps.put("mail.smtp.starttls.enable", "true");
        mailProps.put("mail.smtp.debug", "true");

        sender.setJavaMailProperties(mailProps);

        return sender;
    }

<bean id="mailSender" class ="org.springframework.mail.javamail.JavaMailSenderImpl" >
    <property name="username" value="XXX@gmail.com" />
    <property name="password" value="XXX" />
    <property name="javaMailProperties">
    <props>
        <prop key="mail.smtp.user" value="XXX@gmail.com" />
        <prop key="mail.smtp.password" value="XXX" />
        <prop key="mail.smtp.host">smtp.gmail.com</prop>
        <prop key="mail.smtp.port">587</prop>
        <prop key="mail.smtp.auth">true</prop>
        <prop key="mail.smtp.starttls.enable">true</prop>
    </props>
    </property>
</bean>

<bean id="mailSender" class="org.springframework.mail.javamail.JavaMailSenderImpl">
    <property name="host" value="smtp.gmail.com" />
    <property name="port" value="465" />
    <property name="protocol" value="smtps" />
    <property name="username" value="my_email@domain.tld" />
    <property name="password" value="my_password" />
    <property name="javaMailProperties">
    <props>
        <prop key="mail.smtps.auth">true</prop>
    </props>
    </property>
</bean>

spring.mail:
  host: smtp.gmail.com
  port: 465
  protocol: smtp
  username: xyz@gmail.com
  password: abc
  test-connection: true
  properties:
    "mail.smtp.auth": true
    "mail.smtp.starttls.enable": true
    "mail.smtp.starttls.required": true
    "mail.smtp.socketFactory.class": javax.net.ssl.SSLSocketFactory
    "mail.debug": true