Spring Boot Email Sending Application with Multiple Attachments, CC, BCC, and Rich Text Editor

Sending emails is a common requirement in modern applications for notifications, alerts, customer communication, report sharing, and contact forms. In this tutorial, we will build a complete Spring Boot email sending application using Gmail SMTP.

The application supports multiple recipients, CC, BCC, rich HTML email content, multiple file attachments, asynchronous email processing, validation, logging, and a responsive Bootstrap-based user interface.

The complete source code is available on GitHub, and this article focuses on the project architecture, configuration, application flow, and execution steps.

Prerequisites

Before starting, ensure the following software is installed:

• Java 25
• Maven 3.9+
• IntelliJ IDEA / Eclipse / VS Code
• Gmail Account
• Modern Web Browser (Chrome, Edge, Firefox)

Project Structure

email-sending-with-attachments
│
├── src
│   ├── main
│   │   ├── java
│   │   │   └── com.javacodepoint.email
│   │   │       ├── config
│   │   │       ├── constant
│   │   │       ├── controller
│   │   │       ├── dto
│   │   │       ├── exception
│   │   │       ├── service
│   │   │       ├── validator
│   │   │       └── EmailSendingWithAttachmentsApplication.java
│   │   │
│   │   └── resources
│   │       ├── static
│   │       │   ├── css
│   │       │   └── js
│   │       │
│   │       ├── templates
│   │       │   └── index.html
│   │       │
│   │       └── application.properties
│   │
│   └── test
│
├── pom.xml
│
└── README.md

Gmail App Password Configuration

Google no longer allows applications to access Gmail accounts using your normal Gmail password.

Instead, you must generate an App Password.

Step 1: Enable Two-Factor Authentication

Open your Google Account settings.

Navigate to:

Security → 2-Step Verification

Enable two-factor authentication.

Step 2: Generate App Password

Navigate to:

Security → App Passwords

Create a new App Password.

Example:

abcd efgh ijkl mnop

Copy this password and keep it safe.

Step 3: Configure application.properties

spring.mail.host=smtp.gmail.com
spring.mail.port=587
spring.mail.username=your-email@gmail.com
spring.mail.password=your-app-password

spring.mail.properties.mail.smtp.auth=true
spring.mail.properties.mail.smtp.starttls.enable=true

spring.servlet.multipart.max-file-size=10MB
spring.servlet.multipart.max-request-size=20MB

Replace the username and password values with your Gmail credentials and the generated App Password.

Application Architecture

The application follows a layered architecture.

Frontend Layer

The frontend is built using:

• Bootstrap 5
• Quill Rich Text Editor
• Pure JavaScript

Responsibilities:

• Collect email information
• Upload attachments
• Perform basic validation
• Submit data to the backend

Controller Layer

The controller receives requests from the UI and converts uploaded files into attachment DTOs.

Responsibilities:

• Accept form data
• Receive uploaded files
• Build EmailAttachment DTOs
• Invoke the service layer

Service Layer

The service performs validation and sends emails asynchronously.

Responsibilities:

• Validate recipient emails
• Validate attachment size
• Validate attachment type
• Build MIME message
• Send email through Gmail SMTP

Async Processing

The application uses:

@Async("emailExecutor")

This prevents the UI from waiting for Gmail SMTP operations and improves user experience.

Important Source Files

EmailController

Responsible for receiving email requests from the frontend and converting uploaded files into attachment DTOs.

EmailService

Contains the business logic for:

• Email validation
• Attachment validation
• HTML email creation
• Sending emails asynchronously

AsyncConfig

Configures the thread pool used for background email processing.

EmailAttachment

DTO is used to safely transfer attachment data between threads.

application.properties

Contains Gmail SMTP and file upload configurations.

Source Code

For the complete source code, download the project from the GitHub repository.

Application Flow

The following flow illustrates how the application works.

Running the Application

Start the application using Maven:

mvn spring-boot:run

Or run the main class directly from IntelliJ IDEA.

Open Browser

http://localhost:8080

The Email Sending Application UI should appear.

Test Email Sending

1. Enter recipient email addresses.
2. Add CC or BCC recipients if required.
3. Enter subject.
4. Compose HTML email content.
5. Upload attachments.
6. Click Send Email.

The application will process the email asynchronously and deliver it through Gmail SMTP.

Conclusion

In this tutorial, we built a complete Email Sending Application using Spring Boot, Gmail SMTP, Bootstrap, and JavaScript. The application supports HTML emails, multiple recipients, multiple attachments, asynchronous processing, validation, and proper exception handling.

This project can be used as a foundation for contact forms, notification systems, report delivery services, customer communication platforms, and other real-world applications that require email functionality.

Feel free to download the source code, customize the application, and integrate it into your own projects.