📧 EmailService

A lightweight Spring Boot microservice that consumes email messages from a Kafka topic and sends them via SMTP. Ideal for building scalable, event-driven architectures with email capabilities.

---

🚀 Features

• Kafka Consumer: Listens to the signup topic (or others).
• SMTP Email Delivery: Sends emails with TLS/SSL encryption.
• Environment-driven configuration: Externalize credentials via environment variables.
• Simple & Focused: Single responsibility — email delivery.

---

🧩 Tech Stack

• Java 17
• Spring Boot
• Spring for Kafka
• Apache Kafka
• JavaMail (SMTP)
• Jackson (ObjectMapper)
• Maven

---

📁 Project Structure

src/

├── main/

│ ├── java/com/example/emailservice/

│ │ ├── clients/

│ │ │ └── KafkaConsumerEmailClient.java # Kafka listener & email sender

│ │ ├── dtos/

│ │ │ └── EmailDto.java

│ │ └── utils/

│ │ └── EmailUtil.java

│ └── resources/

│ └── application.properties # Configurations

---

🛠️ Prerequisites

1. Java 17+
2. Kafka running (e.g., localhost:9092)
3. SMTP server credentials (Gmail, Outlook, custom)
4. Environment variables (or a .env file with dotenv support)

---

⚙️ Setup & Configuration

Place the real application.properties in src/main/resources/ or use a .env:

Properties

Kafka

spring.kafka.bootstrap-servers=localhost:9092

spring.kafka.consumer.group-id=emailService

SMTP (Injected via environment)

smtp.mail=smtp.gmail.com

smtp.port=587

email.username=${EMAIL_USERNAME}

email.password=${EMAIL_PASSWORD}

---

⚙️ Running the Service

1. Build the project

./mvnw clean install

2. Run the microservice

./mvnw spring-boot:run

---

🔧 Customize & Extend

1. Add additional @KafkaListener(topic = "otherTopic", ...) methods for more email scenarios.

2. Use @Header(KafkaHeaders.RECEIVED_TOPIC) to differentiate message types inside a listener.

3. Add unit tests using JUnit & Mockito to validate consumer logic and error handling.

---

🧠 Troubleshooting

1. "Could not resolve placeholder" errors → Ensure env vars or application.properties are correctly set.

2. No connection to Kafka → Verify bootstrap-servers and that Kafka is running.

3. Email authentication errors → Check SMTP settings and correct credentials.

---

Security Best Practices

1. ❌ Never commit real credentials.

2. ✅ Use environment variables or secret managers.

3. ✅ Add application.properties and .env to .gitignore.

---

License & Author

Author: Harshal Kalewar

Project: EmailService

License: MIT

GitHub: @harshalkalewar

---

Contributions

Contributions and suggestions are welcome! Please open issues or PRs.

---