Przykłady kodu do wpisu o Spring Mail znajdującego się pod adresem: https://blog.mloza.pl/spring-mail-spring-boot-latwe-wysylanie-maili-z-aplikacji-w-javie/

email.html

<h1>Cześć {{ username }}</h1>
<p>To jest przykładowy e-mail!</p>
<p>
<a href="https://blog.mloza.pl" target="_blank" style="display: inline-block; color: #ffffff; background-color: #3498db;
border: solid 1px #3498db; border-radius: 5px; box-sizing: border-box; cursor: pointer; text-decoration: none;
font-size: 14px; font-weight: bold; margin: 0 auto; padding: 12px 25px; border-color: #3498db;">Podoba mi się!</a>
</p>

--<br>
Pozdrawiam!<br>
Michał z blog.mloza.pl

HtmlMailService.java

    public void sendHtmlEmail(String to, String subject, String content) {
        MimeMessage mail = javaMailSender.createMimeMessage();
        try {
            MimeMessageHelper helper = new MimeMessageHelper(mail, true);
            helper.setTo(to);
            helper.setFrom("Blog example <from@email.com>");
            helper.setSubject(subject);
            helper.setText(content, true);
        } catch (MessagingException e) {
            e.printStackTrace();
        }
        javaMailSender.send(mail);
    }

MailController.java

@RestController
public class MailController {

    private MailService mailService;

    public MailController(MailService mailService) {
        this.mailService = mailService;
    }

    @GetMapping("/sendemail")
    public String sendEmail() {
        mailService.sendSimpleEmail("Odbiorca <odbiorca@maila.pl>", "Test e-mail", "Testing email functionality");

        return "E-mail sent!";
    }
}

MailService.java

@Service
public class MailService {

    private JavaMailSender javaMailSender; // 1

    public MailService(JavaMailSender javaMailSender) {
        this.javaMailSender = javaMailSender;
    }

    public void sendSimpleEmail(String to, String subject, String content) {
        SimpleMailMessage msg = new SimpleMailMessage();
        msg.setTo(to);
        msg.setFrom("Blog Example <from@email.com>");
        
        msg.setSubject(subject);
        msg.setText(content);

        javaMailSender.send(msg);
    }
}

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>pl.mloza</groupId>
    <artifactId>spring-mail</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-dependencies</artifactId>
                <type>pom</type>
                <version>2.1.6.RELEASE</version>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-mail</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.6.2</version>
                <configuration>
                    <source>10</source>
                    <target>10</target>
                    <release>10</release>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

pom2.xml

        <dependency>
            <groupId>org.jtwig</groupId>
            <artifactId>jtwig-core</artifactId>
            <version>5.87.0.RELEASE</version>
        </dependency>

SendHtmlEmail.java

    @GetMapping("/sendhtmlemail")
    public String sendHtmlEmail() {
        JtwigTemplate emailTemplate = JtwigTemplate.classpathTemplate("email/htmlEmail.twig");
        JtwigModel model = JtwigModel.newModel()
                .with("username", "Michał");

        String emailMessage = emailTemplate.render(model);

        mailService.sendHtmlEmail("Michal <michal@mloza.pl>", "Test e-mail", emailMessage);

        return "E-mail sent!";
    }