Skip to content

Latest commit

 

History

History
112 lines (78 loc) · 5.07 KB

README.md

File metadata and controls

112 lines (78 loc) · 5.07 KB
Raw

HollerTP (SMTP Protocol)

Project Description

HollerTP is an SMTP (Simple Mail Transfer Protocol) mail service implemented in C. The project aims to provide a lightweight, efficient, and fully functional SMTP server that can handle basic email sending operations. Designed to be fast and secure, hollertp serves as a fundamental tool for understanding the core principles of email transmission over the internet.

Goals

  • Learn and Implement SMTP Protocol: Understand the SMTP protocol in depth and implement it from scratch using the C programming language.
  • Create a Lightweight SMTP Server: Develop a simple yet powerful SMTP server that can send emails efficiently.
  • Enhance Security: Incorporate basic security measures, such as input validation and proper error handling, to prevent common vulnerabilities.
  • Optimize for Performance: Ensure the server is optimized for performance, capable of handling multiple email requests concurrently.

Specifications

  • Protocol: SMTP (RFC 5321)
  • Programming Language: C
  • Concurrency: The server will handle multiple connections using multi-threading or select/poll-based multiplexing.
  • Security: Basic input validation, error handling, and potential TLS/SSL support (optional).
  • Supported Platforms: Unix-based systems (Linux, macOS), with potential Windows support.

Prerequisites

  • GCC Compiler: Ensure that GCC is installed on your system.
  • PowerShell: Use PowerShell as an administrator to run some commands, particularly on Windows.
  • Administrator Privileges: Required to bind the server to port 25.

Design

Architecture

  1. Connection Handling:

    • The server listens on a designated port (typically port 25 for SMTP) and accepts incoming client connections.
    • Each connection is handled in a separate thread or using an event-driven approach (e.g., select, poll).

  2. SMTP Commands Implementation:

    • The server processes standard SMTP commands such as HELO/EHLO, MAIL FROM, RCPT TO, DATA, QUIT, etc.
    • The server responds with appropriate status codes based on the SMTP protocol.

  3. Email Data Processing:

    • The server receives email data and processes it according to SMTP rules.
    • It will parse headers, handle message bodies, and prepare the email for delivery.

  4. Security Measures:

    • Basic input validation to prevent command injection.
    • Proper error handling to avoid buffer overflows and other common C vulnerabilities.
    • Optional TLS/SSL support for secure email transmission.

  5. Logging:

    • Implement a logging mechanism to track server activity, errors, and connection details.

  6. Future Enhancements (Optional):

    • Add TLS/SSL support for encrypted communication.
    • Implement an email queuing system for delayed delivery.
    • Develop a web-based dashboard for monitoring server activity.

Current Status

  • The server currently supports basic SMTP commands: HELO/EHLO, MAIL FROM, RCPT TO, DATA, and QUIT.
  • The server currently handles connections sequentially in a single-threaded manner. Multi-threading or event-driven concurrency is planned for future updates.
  • Basic input validation is in place. More advanced security features, including comprehensive error handling and potential TLS/SSL support, are being tried to implement.
  • This application is currently Windows supported as I crashed my linux 3 days ago for running a command that was intended to remove a file but... well.
  • This now logs every single command with the date and time and records all transfers of mails.
  • This is only a simulator that simulates how an SMTP server works.

How to Build and Run

  1. Clone the Repository:

    git clone https://github.com/hollermay/hollertp.git
cd hollertp

  2. Build the Project: To compile the SMTP server code, use GCC. Run this command in PowerShell with administrator privileges:

    gcc smtp.c loglib.c -o smtp.exe -lws2_32

    This command compiles the smtp.c file into an executable named smtp.exe.

  3. Run the SMTP Server: After building the project, run the server executable:

    .\smtp

    Make sure to run this command as an administrator, as the server needs appropriate permissions to bind to port 25. NOTE:If this doesn't work reveal the executable file in explorer then run it as administrator.

  4. Test the SMTP Server: You can test the server using an email client or command-line tools like telnet or netcat.

    telnet localhost 25

    You can manually input SMTP commands like HELO, MAIL FROM, RCPT TO, DATA, and QUIT to interact with the server..

License

This project is licensed under the MIT License. See the LICENSE file for details.

Contributions

Contributions are welcome! Feel free to fork the repository, create a branch, and submit a pull request.

References

Below are the references I used while building the project.

https://blog.thelifeofkenneth.com/2012/06/minimalist-c-smtp-mail-server.html https://www.cloudflare.com/learning/email-security/what-is-smtp/