High-Performance gRPC Mail & OTP Server

A high-concurrency microservice built with Go and gRPC to handle email delivery and OTP management.

🎯 Core Problem & Solution

• The Problem: Standard net/smtp is slow because it creates a new connection (TCP handshake + TLS + Auth) for every single email sent.
• Our Solution: Implements a Worker Pool with Persistent Connections. Workers pre-dial and stay authenticated, allowing emails to be dispatched instantly with zero handshake latency.

⚡ Key Features

• Zero-Latency Sending: Persistent SMTP connections eliminate handshake overhead.
• Concurrency: Configurable worker pool (default: 5) handles multiple clients simultaneously without blocking.
• Thread-Safe OTP: In-memory storage protected by sync.RWMutex with atomic validation logic to prevent race conditions.
• Auto-Cleanup: Background "Janitor" worker removes expired OTPs to prevent memory leaks.
• Graceful Shutdown: Completes active jobs before closing connections on SIGINT or SIGTERM.

⚙️ Configuration (.env)

PORT=40700
WORKERS=5                # Concurrent SMTP connections
OTP_CLEANUP_MINUTES=5    # Expiry check interval

# SMTP Settings (e.g., Gmail)
EMAIL_HOST=smtp.gmail.com
EMAIL_PORT=465
EMAIL=your_email@gmail.com
APP_PASSWORD=xxxx-xxxx-xxxx-xxxx

🚀 Usage

1. Setup

go mod tidy
make generate  # Re-generates Protobuf code

2. Run

go run main.go

📚 API Overview

OtpService

Method	Inputs	Description
SendCode	email	Generates a 6-digit code, stores it in memory, and dispatches an email via the worker pool.
ValidateCode	email, otp	Thread-safe validation. Automatically deletes the code upon success to prevent replay attacks.

MailService

Method	Inputs	Description
SendMail	to, subject, body	Asynchronously queues a raw email to be processed by the next available worker.