DevSmtp

A lightweight SMTP server for developers to test email functionality in their applications. DevSmtp captures all emails sent to it and stores them in a SQLite database, providing a terminal-based UI for viewing and managing messages.

Features

• Full SMTP Support - Implements all standard SMTP commands (HELO, EHLO, MAIL FROM, RCPT TO, DATA, RSET, NOOP, QUIT, VRFY, EXPN)
• STARTTLS Support - Optional TLS encryption via STARTTLS
• Configurable Authentication - SMTP AUTH support with configurable credentials (optional or required)
• SQLite Storage - All messages stored locally in a SQLite database
• Terminal UI - Built-in TUI for browsing and inspecting captured emails
• Flexible Configuration - Configure via CLI flags, environment variables, or config file

Installation

From Source

git clone https://github.com/lawnchairsociety/devsmtp.git
cd devsmtp
go build -o devsmtp ./cmd/devsmtp

Go Install

go install github.com/lawnchairsociety/devsmtp/cmd/devsmtp@latest

Usage

# Start with default settings (port 587)
devsmtp

# Start on a custom port
devsmtp --port 2525

# Start with authentication required
devsmtp --auth-required --auth-user testuser --auth-pass testpass

This launches both the SMTP server and the terminal UI. The TUI displays incoming emails in real-time.

Configuration

DevSmtp can be configured through CLI flags, environment variables, or a configuration file. Priority order: CLI flags > environment variables > config file > defaults.

CLI Flags

Flag	Description	Default
--port	SMTP server port	587
--host	SMTP server bind address	0.0.0.0
--db	SQLite database path	./devsmtp.db
--auth-required	Require SMTP authentication	false
--auth-user	Username for SMTP AUTH	``
--auth-pass	Password for SMTP AUTH	``
--tls-cert	Path to TLS certificate	``
--tls-key	Path to TLS private key	``
--config	Path to config file	./devsmtp.yaml

Environment Variables

Variable	Description
DEVSMTP_PORT	SMTP server port
DEVSMTP_HOST	SMTP server bind address
DEVSMTP_DB	SQLite database path
DEVSMTP_AUTH_REQUIRED	Require SMTP authentication
DEVSMTP_AUTH_USER	Username for SMTP AUTH
DEVSMTP_AUTH_PASS	Password for SMTP AUTH
DEVSMTP_TLS_CERT	Path to TLS certificate
DEVSMTP_TLS_KEY	Path to TLS private key

Config File

Create a devsmtp.yaml file:

server:
  host: "0.0.0.0"
  port: 587

database:
  path: "./devsmtp.db"

auth:
  required: false
  username: ""
  password: ""

tls:
  cert: ""
  key: ""

SMTP Commands

DevSmtp implements the following SMTP commands per RFC 5321:

Command	Description
HELO	Identify client (basic)
EHLO	Identify client (extended)
MAIL FROM	Specify sender address
RCPT TO	Specify recipient address
DATA	Begin message content
RSET	Reset session state
NOOP	No operation (keep-alive)
QUIT	End session
VRFY	Verify address (returns 252)
EXPN	Expand mailing list (returns 252)
STARTTLS	Upgrade to TLS connection
AUTH	Authenticate (PLAIN, LOGIN)

TUI Features

The terminal UI provides:

• List view of all captured emails
• View full email headers and body
• Delete individual or all messages
• Real-time updates as new emails arrive

Database Schema

Messages are stored in SQLite with the following schema:

CREATE TABLE messages (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    sender TEXT NOT NULL,
    recipients TEXT NOT NULL,
    subject TEXT,
    body TEXT,
    raw_data BLOB,
    size INTEGER NOT NULL DEFAULT 0,
    client_ip TEXT,
    is_read BOOLEAN NOT NULL DEFAULT 0,
    created_at DATETIME DEFAULT CURRENT_TIMESTAMP
);

CREATE INDEX idx_messages_created_at ON messages(created_at);
CREATE INDEX idx_messages_is_read ON messages(is_read);

Development

Prerequisites

• Go 1.21 or later

Building

go build -o devsmtp ./cmd/devsmtp

Running Tests

go test ./...

License

MIT License - see LICENSE for details.