simple_email - SMTP Email Library for Eiffel

Overview

simple_email is a production-ready SMTP email library for Eiffel with TLS encryption using native Windows SChannel (no OpenSSL dependency). It supports STARTTLS upgrade, implicit TLS (port 465), AUTH PLAIN/LOGIN authentication, and MIME multipart messages with attachments.

Part of the Simple Eiffel ecosystem.

Quick Start

Installation

Set the environment variable:
```
export SIMPLE_EIFFEL=/d/prod
```

Add to your ECF file:

<library name="simple_email" location="$SIMPLE_EIFFEL/simple_email/simple_email.ecf"/>

Send an Email

local
    email: SIMPLE_EMAIL
    msg: SE_MESSAGE
do
    create email.make

    -- Configure SMTP server
    email.set_smtp_server ("smtp.gmail.com", 587)
    email.set_credentials ("user@gmail.com", "app-password")

    -- Connect with STARTTLS
    email.connect
    email.start_tls
    email.authenticate

    -- Create message
    msg := email.create_message
    msg.set_from ("user@gmail.com")
    msg.add_to ("recipient@example.com")
    msg.set_subject ("Hello from Eiffel!")
    msg.set_text_body ("This email was sent using simple_email.")

    -- Send
    if email.send (msg) then
        print ("Email sent successfully!")
    end

    email.disconnect
end

Key Features

TLS Encryption

Native Windows SChannel - no OpenSSL dependency required.

STARTTLS Support

Upgrade plain connections to encrypted on port 587.

Implicit TLS

Direct encrypted connections on port 465.

Authentication

AUTH PLAIN and AUTH LOGIN mechanisms supported.

MIME Multipart

Text + HTML bodies and file attachments.

Security Hardened

Input validation prevents CRLF injection attacks.

API Reference

SIMPLE_EMAIL - Facade Class

Method	Description
`set_smtp_server (host, port)`	Configure SMTP server hostname and port
`set_credentials (user, pass)`	Set authentication credentials
`connect`	Connect to server (plain connection)
`connect_tls`	Connect with implicit TLS (port 465)
`start_tls`	Upgrade connection to TLS (STARTTLS)
`authenticate`	Authenticate with stored credentials
`send (message)`	Send email message, returns success boolean
`create_message`	Factory for new SE_MESSAGE
`disconnect`	Close connection

SE_MESSAGE - Email Message

Method	Description
`set_from (address)`	Set sender address (validated)
`add_to (address)`	Add To recipient
`add_cc (address)`	Add Cc recipient
`add_bcc (address)`	Add Bcc recipient
`set_subject (text)`	Set subject line
`set_text_body (text)`	Set plain text body
`set_html_body (html)`	Set HTML body
`attach_file (path)`	Attach file from path
`attach_data (name, type, data)`	Attach inline data
`is_valid`	True if has from + recipients

Security

simple_email uses Design by Contract to enforce input validation. All email addresses must:

Not be empty
Contain an @ symbol
Not contain CR or LF characters (prevents CRLF injection)

The library has been security hardened with:

10 adversarial tests (injection, boundary, state attacks)
6 stress tests (1000 recipients, 100 attachments, 1MB bodies)
15 DBC contracts protecting critical operations

Class Structure

Class	Purpose
`SIMPLE_EMAIL`	High-level facade for sending email
`SE_MESSAGE`	Email message with headers, body, attachments
`SE_ATTACHMENT`	File or inline attachment
`SE_SMTP_CLIENT`	Full SMTP protocol implementation
`SE_TLS_SOCKET`	WinSock + SChannel TLS socket