Introduction

During this exercise we will use the Spring Boot Starter for sending mail

Background info

Some definitions

Spring Boot Starters are all those dependencies which are started with spring-boot-starter and are used in Spring Boot to get you started with some part of the Spring framework e.g. Data, JDBC, Test and Web

Links

Overview for sending email using Spring Boot Starter Mail

In this article, we’ll walk through the steps needed to send emails from both a plain vanilla Spring application as well as from a Spring Boot application, the former using the JavaMail library and the latter using the spring-boot-starter-mail dependency.

Maven dependencies

First, add the following Maven dependencies
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-mail</artifactId>
</dependency>

Mail Server Properties

The interfaces and classes for Java mail support in the Spring framework are organized as follows

  • MailSender interface

    • The top-level interface that provides basic functionality for sending simple emails

  • JavaMailSender interface

    • the subinterface of the above MailSender. It supports MIME messages and is mostly used in conjunction with the MimeMessageHelper class for the creation of a MimeMessage. It’s recommended to use the MimeMessagePreparator mechanism with this interface

  • JavaMailSenderImpl class

    • provides an implementation of the JavaMailSender interface. It supports the MimeMessage and SimpleMailMessage

  • SimpleMailMessage class

    • used to create a simple mail message including the from, to, cc, subject and text fields

  • MimeMessagePreparator interface

    • provides a callback interface for the preparation of MIME messages

  • MimeMessageHelper class

    • helper class for the creation of MIME messages. It offers support for images, typical mail attachments and text content in an HTML layout

In the following sections, we show how these interfaces and classes are used

Spring Mail Server Properties

Mail properties that are needed to specify e.g. the SMTP server may be defined using the JavaMailSenderImpl.

For example, for Gmail this can be configured as shown below
@Bean
public JavaMailSender getJavaMailSender() {
    JavaMailSenderImpl mailSender = new JavaMailSenderImpl();
    mailSender.setHost("smtp.gmail.com");
    mailSender.setPort(587);

    mailSender.setUsername("my.gmail@gmail.com");
    mailSender.setPassword("password");

    Properties props = mailSender.getJavaMailProperties();
    props.put("mail.transport.protocol", "smtp");
    props.put("mail.smtp.auth", "true");
    props.put("mail.smtp.starttls.enable", "true");
    props.put("mail.debug", "true");

    return mailSender;
}

Spring Boot Mail Server Properties

Once the dependency is in place, the next step is to specify the mail server properties in the application.properties file using the spring.mail.* namespace.

For example, the properties for Gmail SMTP Server can be specified as
spring.mail.host=smtp.gmail.com
spring.mail.port=587
spring.mail.username=<login user to smtp server>
spring.mail.password=<login password to smtp server>
spring.mail.properties.mail.smtp.auth=true
spring.mail.properties.mail.smtp.starttls.enable=true

Some SMTP servers require a TLS connection, so the property spring.mail.properties.mail.smtp.starttls.enable is used to enable a TLS-protected connection.

Gmail SMTP Properties

We can send an email via Gmail SMTP server. Have a look at the documentation to see the Gmail outgoing mail SMTP server properties.

Our application.the properties file is already configured to use Gmail SMTP (see the previous section).

Note that the password for your account should not be an ordinary password, but an application password generated for your google account. Follow this link to see the details and to generate your Google App Password.

Postfix (Linux) configuration
spring.mail.host=localhost
spring.mail.port=25
spring.mail.username=<your user id>
spring.mail.password=<your password>
spring.mail.properties.mail.smtp.auth=false
spring.mail.properties.mail.smtp.starttls.enable=false

Sending Email

Once dependency management and configuration are in place, we can use the aforementioned JavaMailSender to send an email.

Since both the plain vanilla Spring framework as well as the Boot version of it handle the composing and sending of e-mails in a similar way, we won’t have to distinguish between the two in the subsections below.

Sending Simple Emails

Let’s first compose and send a simple email message without any attachments
@Component
public class EmailServiceImpl {

    @Autowired
    public JavaMailSender emailSender;

    public void sendSimpleMessage(String to, String subject, String text) {
        SimpleMailMessage message = new SimpleMailMessage();
        message.setTo(to);
        message.setSubject(subject);
        message.setText(text);
        emailSender.send(message);
    }
}

Finishing

Add a REST controller which accepts to, subject and text and send it using Postman …​

Done

For this part of the exercise you are done regarding using the spring-boot-starter-mail

Continuation

Only applicable later during working hours, and …​ untested by me …​

Sending Emails with Attachments

Sometimes Spring’s simple messaging is not enough for our use cases.

For example, we want to send an order confirmation email with an invoice attached.

In this case, we should use a MIME multipart message from JavaMail library instead of SimpleMailMessage.

Spring supports JavaMail messaging with the org.springframework.mail.javamail.MimeMessageHelper class.

First of all, we’ll add a method to the EmailServiceImpl to send emails with attachments
@Override
public void sendMessageWithAttachment(
  String to, String subject, String text, String pathToAttachment) {
    // ...

    MimeMessage message = emailSender.createMimeMessage();

    MimeMessageHelper helper = new MimeMessageHelper(message, true);

    helper.setTo(to);
    helper.setSubject(subject);
    helper.setText(text);

    FileSystemResource file
      = new FileSystemResource(new File(pathToAttachment));
    helper.addAttachment("Invoice", file);

    emailSender.send(message);
    // ...
}

Simple Email Template

SimpleMailMessage class supports text formatting. We can create a template for emails by …​

defining a template bean in our configuration
@Bean
public SimpleMailMessage templateSimpleMessage() {
    SimpleMailMessage message = new SimpleMailMessage();
    message.setText(
      "This is the test email template for your email:\n%s\n");
    return message;
}
Now we can use this bean as a template for email and only need to provide necessary parameters to the template
@Autowired
public SimpleMailMessage template;
...
String text = String.format(template.getText(), templateArgs);
sendSimpleMessage(to, subject, text);
...

Handling Send Errors

JavaMail provides SendFailedException to handle situations when a message cannot be sent. But it is possible that you won’t get this exception while sending an email to the incorrect address. The reason is the following:

The protocol specs for SMTP in RFC 821 specifies the 550 return code that SMTP server should return when attempting to send an email to the incorrect address. But most of the public SMTP servers don’t do this. Instead, they send a “delivery failed” email to your box, or give no feedback at all.

For example, Gmail SMTP server sends a “delivery failed” message. And you get no exceptions in your program.

So, there are few options you can go through to handle this case

  • Catch the SendFailedException, which can never be thrown

  • Check your sender mailbox on “delivery failed” message for some period of time. This is not straightforward and the time period is not determined

  • If your mail server gives no feedback at all, you can do nothing

Conclusion

In this quick article, we showed how to set up and send emails from a Spring Boot application.

The implementation of all these examples and code snippets can be found in the GitHub project; this is a Maven-based project, so it should be easy to import and run as it is.

Resources and Credits

Used this to create this page

Guide to Spring Email from Bealdung.com