Mohammad Waseem

Posted on Feb 1

Automating Email Flow Validation with Rust and Open Source Tools

#rust #email #qa

Ensuring reliable email workflows is a critical aspect of quality assurance for modern SaaS applications. As Lead QA Engineer, I adopted an approach leveraging Rust, a systems programming language known for performance and safety, combined with various open source tools, to create a robust, scalable email validation framework.

The Challenge of Validating Email Flows

Email workflows involve multiple components: trigger events, email generation, delivery, and user interaction. Traditional testing may rely on manual checks or basic SMTP command tests, which are insufficient for comprehensive validation—especially at scale. The goal was to automate the process, verify deliverability, content correctness, and timing, while seamlessly integrating into CI/CD pipelines.

Why Rust?

Rust provides unmatched performance, safety, and concurrency features, making it ideal for building a reliable email validation tool. Its strong type system and memory safety eliminate many common bugs, while the rich ecosystem of crates simplifies tasks like network communication, JSON parsing, and concurrency.

Architectural Overview

The solution comprises three main components:

A Rust-based Email Validator Service.
Open source email testing tools like MailHog and Ethereal.
An orchestrator script that manages test flows and reports.

1. Rust Email Validator Service

This service connects to SMTP servers, simulates email sending, and verifies responses.

use std::net::TcpStream;
use std::io::{Write, BufReader, BufRead};

fn send_smtp_command(stream: &mut TcpStream, command: &str) -> std::io::Result<String> {
    writeln!(stream, "{}", command)?;
    let mut reader = BufReader::new(stream);
    let mut response = String::new();
    reader.read_line(&mut response)?;
    Ok(response)
}

fn validate_email_flow(smtp_server: &str, from: &str, to: &str) -> Result<bool, String> {
    let mut stream = TcpStream::connect(smtp_server).map_err(|e| e.to_string())?;
    let hello_response = send_smtp_command(&mut stream, "EHLO localhost")?;
    if !hello_response.starts_with("250") {
        return Err("EHLO failed".into());
    }
    // Further SMTP commands: MAIL FROM, RCPT TO, DATA ...
    // Check responses for correctness
    Ok(true)
}

This code snippet demonstrates connecting to an SMTP server, issuing commands, and analyzing responses to ensure the email flow proceeds correctly.

2. Open Source Email Testing Tools

Tools like MailHog or Ethereal act as intercepting SMTP servers, simulating email delivery environment. They allow us to verify that emails are correctly formed, received, and stored.

MailHog setup example:

docker run -d -p 1025:1025 -p 8025:8025 mailhog/mailhog

Your Rust service can then connect to MailHog’s SMTP endpoint to perform tests.

3. Orchestrator Script

A Python or Bash script can coordinate sending test emails, checking MailHog/Ethereal for incoming messages, and validating email content.

curl -s http://localhost:8025/api/v2/messages | grep -i 'Subject: Welcome'

Integration into CI/CD

By incorporating these components, I set up pipelines that automatically send test emails, analyze delivery timings, and verify content correctness upon each code push. This approach minimizes manual intervention, accelerates testing cycles, and enhances confidence in email workflows.

Key Takeaways

Rust’s performance and safety make it suitable for building robust email validators.
Combining Rust with open source tools like MailHog offers a cost-effective, scalable solution.
Automating email validation within CI/CD pipelines improves quality and reliability.

Investing in such automated tests addresses the complexities of email workflows and ensures consistent user experiences, which are vital for customer engagement and compliance.

References

Rust libraries for network communication: Tokio
MailHog documentation: https://github.com/mailhog/MailHog
Ethereal Email Testing: https://ethereal.email/

Leveraging these tools and approaches transforms manual, error-prone testing into a scalable, reliable process, aligning with best practices in software quality assurance.

🛠️ QA Tip

To test this safely without using real user data, I use TempoMail USA.

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