SMTP Server

Yasumu includes a built-in catch-all SMTP server that captures all emails sent to it, providing a local mailbox for testing email functionality during development. No more sending test emails to real addresses or setting up complex email infrastructure.

Overview

The SMTP server:

• Captures all emails — Acts as a real SMTP server that accepts any email
• Stores locally — Emails are stored in your workspace database
• Provides a mailbox — View, search, and manage received emails in Yasumu
• Works with any library — Compatible with Nodemailer, SendGrid SDK, or any SMTP-capable tool

Accessing the Mailbox

Navigate to Emails in the Yasumu sidebar to access the email features. You'll see two tabs:

Mailbox Features

Email List

The mailbox displays all captured emails with:

• Sender avatar — Color-coded initials based on sender email
• From address — Who sent the email
• Subject line — Email subject (or "No subject" if empty)
• Preview — First 150 characters of the email body
• Timestamp — When the email was received
• Unread indicator — Blue dot for unread emails

Filtering

Filter emails by:

• All — Show all captured emails
• Unread — Show only unread emails

The unread count is displayed as a badge next to the filter.

Email Content

Click an email to view its full content:

• From/To/CC — Full email addresses
• Date — When the email was received
• Subject — Full subject line
• Body — Rendered HTML or plain text content

HTML emails are rendered in a sandboxed iframe for security.

Settings

Server Status

When the SMTP server is running, you'll see a status indicator showing:

• Online status — Green indicator when active
• Active port — The port the server is listening on
• Copy Port — Quick button to copy the port number

Configuration Options

After changing settings, click Save Settings to apply.

Using the SMTP Server

With Nodemailer

The settings page includes a ready-to-use code snippet:

import { createTransport } from 'nodemailer';

const transport = createTransport({
  host: 'localhost',
  port: 2525, // Use the port shown in Yasumu settings
});

await transport.sendMail({
  from: 'sender@example.com',
  to: 'recipient@example.com',
  subject: 'Hello from Yasumu',
  text: 'Hello World!',
});

With Other Libraries

Any SMTP-capable library can send to the Yasumu SMTP server:

Python (smtplib)

import smtplib
from email.message import EmailMessage

msg = EmailMessage()
msg['Subject'] = 'Test Email'
msg['From'] = 'sender@example.com'
msg['To'] = 'recipient@example.com'
msg.set_content('Hello from Python!')

with smtplib.SMTP('localhost', 2525) as smtp:
    smtp.send_message(msg)

Go (net/smtp)

package main

import (
    "net/smtp"
)

func main() {
    msg := []byte("Subject: Test Email\r\n\r\nHello from Go!")
    smtp.SendMail("localhost:2525", nil, "sender@example.com",
        []string{"recipient@example.com"}, msg)
}

Workspace Configuration

SMTP settings are stored in smtp.ysl in your workspace:

@smtp

metadata {
  id: "udlji8yaooo11ud8aetg3omr"
  port: 0
  username: null
  password: null
}

Simulating Rejections

The SMTP server can simulate email rejections for testing error handling. Use email addresses starting with reject (case-insensitive) to trigger a rejection:

// These will be rejected by the SMTP server
await transport.sendMail({
  from: 'reject@example.com',  // Rejected - sender starts with "reject"
  to: 'user@example.com',
  subject: 'This will fail',
  text: 'Never delivered',
});

await transport.sendMail({
  from: 'sender@example.com',
  to: 'rejected@example.com',  // Rejected - recipient starts with "reject"
  subject: 'This will also fail',
  text: 'Never delivered',
});

This is useful for testing:

• Error handling in your email sending code
• Retry logic
• User notifications when emails fail

Real-time Updates

The mailbox automatically refreshes when new emails arrive. No need to manually refresh — emails appear in the list as soon as they're received.

Use Cases

Testing Transactional Emails

await sendPasswordResetEmail(user.email);
// Check Yasumu mailbox to verify email content and formatting

Testing Email Templates

Send emails with different templates to verify:

• HTML rendering
• Dynamic content substitution
• Responsive layouts

Testing Email Workflows

Test multi-step email flows:

• Welcome emails
• Verification emails
• Notification chains

Test environment

Configure your test environment to use Yasumu's SMTP server:

SMTP_HOST=localhost
SMTP_PORT=2525

Best Practices

1. Use port 0 for random — Avoids conflicts with other services
2. Check the active port — The displayed port is what the server is actually using
3. No auth for local dev — Skip username/password for simpler local testing
4. Use auth for shared environments — Add credentials if multiple people access the same instance
5. Clear old emails periodically — Keep the mailbox manageable for performance