integration-mail

Example 11 — Mail Integration

This example demonstrates how to send emails from JavaDelegates using Spring Mail, and how to verify email delivery in integration tests using Mailpit as an SMTP server via Testcontainers.

What you will learn

• How to inject JavaMailSender into a JavaDelegate and compose SimpleMailMessage objects
• How to configure spring-boot-starter-mail in application.yaml
• How to run Mailpit as a Testcontainers GenericContainer for SMTP and API access
• How to verify sent emails by querying the Mailpit REST API from integration tests
• How to model a job-application process with confirmation and decision emails

Process model

Prerequisites

• JDK 21
• Docker (tested with Docker Desktop 4.x and Rancher Desktop 1.x)

Run it

Start the infrastructure:

docker compose up -d

Run the application:

# Make wrappers executable on macOS/Linux
chmod +x mvnw gradlew

./mvnw spring-boot:run
# or
./gradlew bootRun

Access the Operaton web apps at http://localhost:8080 with credentials demo / demo.

The Mailpit web UI is available at http://localhost:8025 — view all sent emails here.

Walk through it

Submit an application:

curl -s -X POST http://localhost:8080/engine-rest/process-definition/key/job-application/start \
  -H "Content-Type: application/json" \
  -d '{
    "variables": {
      "applicantName": {"value": "Jane Doe", "type": "String"},
      "applicantEmail": {"value": "jane@example.com", "type": "String"}
    }
  }'

Open http://localhost:8025 — you should see a confirmation email for Jane Doe.

Approve the application via Tasklist:

1. Open http://localhost:8080/operaton/app/tasklist (demo/demo)
2. Claim the "Review application" task
3. Complete it with variable approved = true

A second email (approval) will appear in Mailpit.

Reject path:

Complete the review task with approved = false to trigger the rejection email ("Application Update").

How it works

• SendConfirmationEmailDelegate (src/main/java/.../delegate/SendConfirmationEmailDelegate.java) — sends a receipt acknowledgement to the applicant as soon as the process starts.
• SendDecisionEmailDelegate (src/main/java/.../delegate/SendDecisionEmailDelegate.java) — sends either an approval or rejection email based on the approved process variable.
• job-application.bpmn (src/main/resources/job-application.bpmn) — models the full workflow: confirmation service task → user task (HR review) → exclusive gateway → decision service task.
• Mailpit is a lightweight SMTP server with a REST API for inspecting received messages. It accepts any email without relay configuration, making it ideal for local development and testing.

Run the tests

./mvnw verify
# or
./gradlew build

JobApplicationProcessIT starts a PostgreSQL container and a Mailpit container via Testcontainers. It proves that:

• Submitting an application sends a confirmation email to the applicant
• Completing the review task with approved = true sends an approval email
• Completing the review task with approved = false sends a rejection email