Guides / Spring Boot

Test Spring Boot emails locally

RustMail is a local SMTP mail catcher. Your Java app keeps sending mail the way it does in production, and every message lands in a web UI instead of a real inbox. Four steps, about two minutes.

1. 1

   Start RustMail

   One container, SMTP on port 1025 and the web UI on 8025.

   docker run -p 1025:1025 -p 8025:8025 smyile/rustmail:latest

2. 2

   Point Spring Boot at it

   In application.properties, send mail to localhost:1025 with no TLS and no credentials.

   spring.mail.host=localhost
   spring.mail.port=1025
   spring.mail.properties.mail.smtp.auth=false
   spring.mail.properties.mail.smtp.starttls.enable=false

3. 3

   Send a test email

   Then open localhost:8025: the message is already in the inbox, with its HTML, headers and links.

   SimpleMailMessage message = new SimpleMailMessage();
   message.setFrom("[email protected]");
   message.setTo("[email protected]");
   message.setSubject("Welcome");
   message.setText("Hello from Spring Boot");
   mailSender.send(message);

4. 4

   Assert on it in CI

   In GitHub Actions, start RustMail, run tests that send mail with the application.properties settings from step 2, then fail the job when the email never arrives.

   - name: Start RustMail on localhost:1025
     uses: rustmailapp/rustmail-action@v1
     with:
       mode: start
   
   - name: Run the tests that send mail over SMTP
     run: ./mvnw verify
     env:
       SPRING_MAIL_HOST: "localhost"
       SPRING_MAIL_PORT: "1025"
   
   - name: Fail if the welcome email never arrived
     uses: rustmailapp/rustmail-action@v1
     with:
       mode: assert
       assert-count: 1
       assert-subject: "Welcome"