> ## Documentation Index
> Fetch the complete documentation index at: https://documentation.mysmtp.com/llms.txt
> Use this file to discover all available pages before exploring further.

# SMTP Limits, Sending Rates and Optimization

> Understand mySMTP sending limits, IP warming strategies, rate limits by provider, and best practices for high-volume email delivery.

## 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)

<Note>
  Exceeding limits may result in:

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

## 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)

| Day | Max Emails Per Day |
| - | - |
| 1-3 | 1,000 |
| 4-6 | 5,000 |
| 7-10 | 10,000 |
| 11-14 | 25,000 |
| 15-20 | 50,000 |
| 21+ | Full quota (100,000) |

<Note>
  **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.**
</Note>

## 3. SMTP Rate Limiting by Destination

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

| Email Provider | Max Per Hour (New IPs) | Max Per Hour (Warmed-Up IPs) | Daily Limit (Estimate) |
| - | - | - | - |
| **Gmail** | 500-1,000 | 5,000+ | 50,000 |
| **Yahoo** | 1,000 | 10,000+ | 100,000 |
| **Outlook/Hotmail** | 500 | 3,000+ | 30,000 |
| **AOL** | 500 | 5,000+ | 50,000 |
| **iCloud Mail** | 500 | 2,000+ | 10,000 |
| **GSuite/Exchange** | Varies | Varies | Varies |

<Note>
  **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).
</Note>

## 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:

| Error Code | Meaning | Solution |
| - | - | - |
| **421** | Too many connections | Lower send rate, retry later |
| **450** | Mailbox unavailable | Retry later |
| **451** | Server overload | Slow down sending speed |
| **550** | Blocked/rejected | Remove bad emails, improve reputation |
| **554** | Marked as spam | Improve content, check domain reputation |

<Note>
  **Pro Tip:** Enable **SMTP logs** in your email software to track failures.
</Note>

## 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).

<Note>
  **Enterprise users can request custom rate limits** and **priority SMTP queues** via mySMTP support.
</Note>

## 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.


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