This is the KB page for administrators.

SMTP Status Codes and Their Meanings

SMTP response codes are three-digit numbers that indicate the status of an email transaction. The first digit defines the response category:

• 1xx – Informational (not commonly used in SMTP)
• 2xx – Success (The request was successfully processed)
• 3xx – Redirection (Additional action required)
• 4xx – Temporary failure (The request failed, but retry may succeed)
• 5xx – Permanent failure (The request failed, do not retry)

Here’s a breakdown of common SMTP status codes:

2xx – Success Codes

These indicate that the email transaction was successfully processed.

• 200 – Nonstandard success response (rarely used).
• 211 – System status or help reply (provides server info).
• 214 – Help message (returns helpful information).
• 220 – SMTP server ready (indicates the server is ready to process requests).
• 221 – SMTP server closing connection (indicates the session is ending).
• 250 – Requested action completed successfully (most common success response).
• 251 – Recipient not local, will forward (email will be relayed to another domain).

3xx – Intermediate/Redirection Codes

These codes indicate that the server expects further input from the client before completing the request.

• 334 – Server response to an authentication request (challenges the client for credentials).
• 354 – Start mail input (indicates the server is ready to receive the email body).

4xx – Temporary Failures

These errors indicate a transient issue that may resolve itself. The sender should retry later.

• 400 – Generic temporary error.
• 421 – Service not available (server is shutting down or overloaded).
• 450 – Requested action not taken because the recipient’s mailbox is unavailable (e.g., mailbox full).
• 451 – Requested action aborted due to a server error (e.g., system overload).
• 452 – Insufficient system storage (server cannot process the email due to lack of resources).

5xx – Permanent Failures

These indicate a permanent error, meaning the request cannot be fulfilled. The sender should not retry.

• 500 – Syntax error (server did not recognize the command).
• 501 – Syntax error in parameters (invalid email address or malformed command).
• 502 – Command not implemented (server does not support the requested command).
• 503 – Bad sequence of commands (commands sent in the wrong order).
• 504 – Command parameter not implemented (server does not recognize a specific parameter).
• 550 – Mailbox unavailable (e.g., recipient does not exist).
• 551 – User not local (server cannot relay the message).
• 552 – Mailbox full (message storage limit exceeded).
• 553 – Invalid recipient address (email address incorrect or malformed).
• 554 – Transaction failed (email rejected, often due to spam filters or security policies).

Example SMTP Transaction with Status Codes

plaintext

CopyEdit

S: 220 mail.example.com SMTP server ready

C: HELO client.example.com

S: 250 mail.example.com Hello client.example.com

C: MAIL FROM:<This email address is being protected from spambots. You need JavaScript enabled to view it.;

S: 250 OK

C: RCPT TO:<This email address is being protected from spambots. You need JavaScript enabled to view it.;

S: 250 OK

C: DATA

S: 354 Start mail input

C: (Message content)

C: .

S: 250 OK, message accepted for delivery

C: QUIT

S: 221 Goodbye

coming soon

Integrating mySMTP with Web Applications

mySMTP is a powerful SMTP relay service that enhances email deliverability for web applications and e-commerce platforms. This guide will walk you through integrating mySMTP with popular platforms, including WordPress, Magento, WooCommerce, PrestaShop, Joomla, Drupal and others.

Prerequisites

Before integration, ensure you have:

• A mySMTP account with SMTP credentials (host, username, password, and port).
• Access to your website’s admin panel or server.

1. WordPress

Using WP Mail SMTP Plugin

1. Install WP Mail SMTP from the WordPress Plugin Directory.
2. Navigate to WP Mail SMTP → Settings.
3. Under Mailer, select Other SMTP.
4. Enter your mySMTP credentials:
   • SMTP Host: mysmtp.com
   • Encryption: TLS (or SSL if required)
   • Port: 587 (or 465 for SSL)
   • Your mySMTP Username & Password
5. Save changes and test email delivery.

2. Magento

Configure SMTP in Magento Admin

1. Install the MagePal SMTP extension (if needed).
2. Navigate to Stores → Configuration → Advanced → System.
3. Expand Mail Sending Settings and update:
   • Host: mysmtp.com
   • Port: 587
   • Authentication: Login
   • your mySMTP Username & Password
4. Save settings and send a test email.

3. WooCommerce

• Follow the WordPress WP Mail SMTP guide (above).
• Ensure WooCommerce email settings point to the correct sender email.

4. PrestaShop

1. Navigate to Advanced Parameters → Email.
2. Select Set My Own SMTP Parameters.
3. Enter mySMTP credentials and save.

5. Drupal

1. Install the SMTP Authentication Support module.
2. Configure SMTP settings with mySMTP details under Configuration → SMTP Authentication.

6. Joomla

1. Go to System → Global Configuration → Server.
2. Set Mailer to SMTP and enter mySMTP details.

7. OpenCart

1. Navigate to Settings → Mail.
2. Set Mail Engine to SMTP and enter mySMTP details.

8. Laravel (PHP Applications)

1. Update your .env file:

MAIL_MAILER=smtp
MAIL_HOST=smtp.mysmtp.com
MAIL_PORT=587
MAIL_USERNAME=your_username
MAIL_PASSWORD=your_password
MAIL_ENCRYPTION=tls

2. Clear cache and restart the server.

9. Symfony

1. Update your .env file:

MAILER_DSN=smtp://your_username:This email address is being protected from spambots. You need JavaScript enabled to view it.:587

2. Test with bin/console swiftmailer:email:send.

10. Django (Python Applications)

1. Update settings.py:

EMAIL_BACKEND = 'django.core.mail.backends.smtp.EmailBackend'
EMAIL_HOST = 'mysmtp.com'
EMAIL_PORT = 587
EMAIL_USE_TLS = True
EMAIL_HOST_USER = 'your_username'
EMAIL_HOST_PASSWORD = 'your_password'

2. Restart the application.

11. ASP.NET Core

1. Add SMTP settings in appsettings.json:

{
"SmtpSettings": {
"Server": "mysmtp.com",
"Port": 587,
"Username": "your_username",
"Password": "your_password",
"UseSSL": false,
"UseStartTls": true
}
}

2. Inject SMTP settings in your mail service.

12. Ghost (Node.js)

1. Update config.production.json:

"mail": {
     "transport": "SMTP",
     "options": {
          "service": "SMTP",
          "host": "smtp.mysmtp.com",
          "port": 587,
          "auth": {
               "user": "your_username",
                    "pass": "your_password"
               }
          }
     }

2. Restart Ghost.

Conclusion

Integrating mySMTP ensures reliable email delivery across web platforms. If you encounter issues, check firewall settings, test with different ports (25, 587), and enable SMTP logs for debugging.

SMTP Limits, Sending Rates & Optimization

Introduction

SMTP (Simple Mail Transfer Protocol) is the backbone of email communication, but improper use can lead to blocked emails, poor deliverability, and sender reputation damage. mySMTP enforces sending limits, rate controls, and warm-up procedures to protect email servers and ensure messages reach inboxes.

This entry covers:
✅ SMTP limits & sending rates
✅ IP warming strategies
✅ Rate limiting by email provider
✅ MailWizz quota settings
✅ SMTP error codes & troubleshooting
✅ Best practices for high-volume email sending

1. SMTP Sending Limits & Rate Control

Understanding SMTP Limits

SMTP providers enforce limits to prevent abuse. These limits vary based on:

• Subscription Plan (Basic vs. Enterprise)
• IP Type (Dedicated IPs have higher limits than shared IPs)
• Email Volume (Sudden spikes can trigger throttling)
• Recipient Domain (Different providers enforce different limits)
• Bounce & Spam Rate (High bounces lead to automatic slowdowns)

💡 Exceeding limits may result in:

• Temporary throttling (slowing down emails).
• Deferrals (email sent later, not immediately).
• Blocking (emails rejected if too many complaints/bounces).

2. IP Warming: Increasing Limits Gradually

Why Warm Up your IP?

New IPs have no reputation and are monitored closely by email providers (Gmail, Outlook, Yahoo, etc.). Sending too many emails at once from a fresh IP looks suspicious and may lead to temporary blocking or blacklisting.

IP Warming Plan (Example: 100,000 Emails/Day Goal)

📌 Best Practices:
✔ Start with engaged recipients (those who open emails often).
✔ Avoid purchased or scraped email lists (can trigger spam complaints).
✔ Maintain a steady sending schedule (no sudden spikes).
✔ Authenticate emails with SPF, DKIM, and DMARC.

3. SMTP Rate Limiting by Destination

Different email providers enforce their own sending limits, affecting how fast mySMTP can relay messages.

🚀 How to Avoid Rate Limits:
✅ Separate email streams (transactional vs. marketing).
✅ Use subdomains (e.g., news.example.com for campaigns).
✅ Monitor feedback loops (check complaints & bounces).

4. MailWizz Minute Quota Configuration (For Bulk Senders)

MailWizz allows you to control SMTP sending speed to avoid exceeding limits. (in progress)

5. SMTP Error Codes & Troubleshooting

When hitting SMTP limits, you may see these errors:

📌 Pro Tip: Enable SMTP logs in your email software to track failures.

6. Advanced Deliverability Tips

🔹 Improve Reputation & Deliverability:
✔ Use dedicated IPs for high-volume sending.
✔ Segment by recipient domain (separate Gmail, Yahoo, etc.).
✔ Monitor complaint rates (keep spam complaints < 0.3%).
✔ Implement engagement-based sending (send more to users who open emails).

🔹 Avoid Getting Blocked by Gmail & Outlook:
✔ Use SPF, DKIM, and DMARC authentication.
✔ Don’t use spammy words in subject lines (free, win, urgent).
✔ Keep unsubscribe links visible to prevent spam reports.
✔ Monitor Postmaster Tools (Gmail) & SNDS (Microsoft) for complaints.

7. Scaling Beyond Limits (Enterprise Solutions)

If you need to send 1M+ emails/day, consider:

• Multiple mySMTP IPs (rotate between different servers).
• Dedicated sending domains (separate marketing & transactional emails).
• AI-driven sending strategies (adjust rates based on engagement).
• mySMTP postmulti servers (spreading email traffic across multiple IPs).

💡 Enterprise users can request custom rate limits and priority SMTP queues via mySMTP support.

Conclusion

Understanding SMTP limits, warming up IPs, and managing sending rates is critical to avoiding blocks and ensuring high deliverability.

🔹 Need custom SMTP settings or higher limits? Contact mySMTP support for tailored recommendations. 🚀

1. What is a Transactional Email?

A transactional email is an automated message triggered by a user action or system event. These emails provide essential information related to an individual transaction or account activity.

🔹 Examples of Transactional Emails

✅ Order confirmations (e.g., "Your order #12345 has been received")
✅ Password resets (e.g., "Click here to reset your password")
✅ Account verification (e.g., "Verify your email address")
✅ Shipping updates (e.g., "Your package is on the way")
✅ Payment receipts (e.g., "Payment of $49.99 has been processed")

🔹 Best Practices for Transactional Emails

1. Use a dedicated SMTP server for transactional emails
   • Ensures fast and reliable delivery.
   • Avoids delays caused by bulk promotional emails.
2. Authenticate emails with SPF, DKIM, and DMARC
   • Protects against spoofing and improves trust with email providers.
   • Use test.smtp.ai to verify authentication.
3. Send from a subdomain (e.g., notifications.yourdomain.com)
   • Keeps transactional emails separate from marketing emails.
   • Improves sender reputation and deliverability.
4. Ensure low latency
   • Transactional emails should be delivered within seconds after the trigger event.
   • Use a high-performance SMTP relay to reduce delays.
5. Avoid promotional content
   • Keep messages clear, concise, and action-oriented.
   • Including marketing offers may cause deliverability issues.

2. What is a Marketing Email?

A marketing email is designed to promote a product, service, or brand and is sent in bulk to a list of recipients. Unlike transactional emails, marketing emails require user consent (opt-in) to comply with regulations like GDPR, CAN-SPAM, and CCPA.

🔹 Examples of Marketing Emails

✅ Newsletters (e.g., "Our latest industry insights – February edition")
✅ Promotions & discounts (e.g., "Save 20% on your next order")
✅ Product announcements (e.g., "Introducing our new AI-powered SMTP tool")
✅ Re-engagement emails (e.g., "We miss you! Here's a special offer")
✅ Event invitations (e.g., "Join our webinar on email security")

🔹 Best Practices for Marketing Emails

1. Send from a separate domain or subdomain
   • Use marketing.yourdomain.com for marketing emails.
   • Prevents marketing emails from affecting transactional email deliverability.
2. Follow email compliance laws (GDPR, CAN-SPAM, CCPA)
   • Include an unsubscribe link in every email.
   • Get explicit consent (opt-in) before sending promotional emails.
3. Optimize email content for engagement
   • Use personalization (e.g., recipient's name) to increase open rates.
   • Keep subject lines short, clear, and compelling.
   • Use A/B testing to improve performance.
4. Warm up your IP address for high-volume sending
   • Gradually increase the number of emails sent to build a good sender reputation.
   • Monitor bounce rates and adjust sending patterns accordingly.
5. Monitor sender reputation and engagement metrics
   • Use tools like Google Postmaster Tools to track sender score.
   • Remove inactive subscribers to improve email engagement rates.

3. Key Differences Between Transactional and Marketing Emails

4. How to Test Your Email Authentication Setup

Regardless of whether you’re sending transactional or marketing emails, it’s essential to test your email authentication to avoid spam issues.

📌 Use test.smtp.ai to check:
✅ SPF, DKIM, DMARC, and BIMI configuration
✅ Blacklist status
✅ Spam score and deliverability issues

Conclusion

Both transactional and marketing emails play vital roles in email communication. However, they require different SMTP setups, compliance measures, and delivery strategies.

🔹 Transactional emails should be fast, reliable, and free of promotions.
🔹 Marketing emails should comply with legal regulations, be engaging, and use proper segmentation.

By following best practices and properly configuring email authentication (SPF, DKIM, DMARC, and BIMI), you can maximize deliverability and security for both types of emails.