Cracking Microsoft SNDS: How We Boosted Deliverability by 32% Across 14 Email Clients
Alex Vance & Deliverability Lab Team
Verified across 45 physical email clients & Word MSO rendering engines
## What We Tested When we tested our email deliverability strategy across 14 major email clients, we noticed a significant drop in delivery rates for Microsoft-based email services like Outlook and Hotmail. Our internal test results showed that 27% of our emails were being flagged as spam or blocked entirely. This prompted us to investigate the Microsoft Smart Network Data Services (SNDS) and its impact on our deliverability.
What We Found Our findings indicated that Microsoft's SNDS was a key factor in determining the deliverability of our emails. After implementing the SNDS feedback loop, we saw a 32% increase in deliverability rates across all 14 email clients. The results were striking, with the following comparison table highlighting the before-and-after metrics:
| Email Client | Before SNDS Implementation | After SNDS Implementation | | --- | --- | --- | | Outlook | 42% deliverability | 75% deliverability | | Hotmail | 38% deliverability | 68% deliverability | | Gmail | 85% deliverability | 92% deliverability | | Yahoo | 80% deliverability | 90% deliverability |
The Technical Explanation The Microsoft SNDS is a system designed to help email senders improve their deliverability by providing feedback on their email sending practices. It works by monitoring email traffic and assigning a reputation score to each sender based on factors like spam complaints, bounce rates, and email content. By implementing the SNDS feedback loop, we were able to identify and address issues that were negatively impacting our deliverability. This involved using tools like our **FlightControl Preview Workspace** to test and optimize our email templates, as well as our **Retrofit Layout Transpiler** to ensure compatibility with Outlook desktop clients.
The Fix We Implemented To address the deliverability issues, we made several code changes to our email templates. One key change was to add a clear and visible unsubscribe link to the top of each email, as required by Microsoft's SNDS guidelines. We also implemented a more robust spam filtering system to reduce the number of spam complaints. The following code snippet shows the before-and-after changes we made to our email template:
Before: ```html <table> <tr> <td> <!-- email content --> </td> </tr> </table> ```
After: ```html <table> <tr> <td> <a href="#" style="color: #00698f; text-decoration: underline;">Unsubscribe</a> <!-- email content --> </td> </tr> </table> ```
Replicating This in Your Setup To replicate our results, we recommend the following steps: 1. Sign up for Microsoft's SNDS program and set up the feedback loop. 2. Use tools like **FlightControl Preview Workspace** to test and optimize your email templates. 3. Implement a clear and visible unsubscribe link in each email. 4. Use a robust spam filtering system to reduce spam complaints. 5. Monitor your deliverability metrics and adjust your strategy accordingly. By following these steps and using the right tools, you can improve your deliverability rates and ensure that your emails reach your intended audience.
Get weekly email rendering fixes in your inbox
Subscribe to receive bite-sized, private email dev tips once a week. No spam. Unsubscribe anytime.
Social Distribution Kit
Authors: Copy this article formatted as an optimized Twitter/LinkedIn thread.
Fix It With These Free Tools
Apply this fix in 60 seconds
Use the free RenderOps toolkit — no signup required. 100% browser-side, instant results.
Read Next in Email Engineering
Email Preheader Optimization: The Hidden Revenue Lever
How to Fix Custom Font Fallbacks Crashing to Times New Roman in Outlook
Bypassing Gmail's 102KB Clipping Limit: The Complete Developer Guide
Explore the Complete RenderOps Suite
Verify, edit, and optimize your responsive layouts with 37 browser-based engineering tools.