A Quick Guide to SNDS

Kristen Wyatt on May 27, 2025

Deliverability is arguably a cornerstone factor for most businesses that rely on email marketing, transactional messages, or any form of email communication. Microsoft (which powers Outlook, Hotmail, Live, and MSN) employs strict spam filters to protect its users. To help legitimate senders monitor their performance, Microsoft offers the Smart Network Data Services (SNDS) platform.

In this blog, we’ll explore what SNDS is, the key metrics it can provide, and best practices to maintain a strong sending reputation with Microsoft’s services. By following these guidelines, you can improve inbox placement and avoid being flagged, throttled, or even blocked.

SNDS is a free analytics tool designed to help email senders monitor their performance across Microsoft’s network. It provides guidance for how Microsoft’s spam filters are handling your mail, allowing you to identify and resolve potential issues before they hurt your overall deliverability.

To start using SNDS, you first need to sign up at https://snds.microsoft.com. After registering, you should add your sending IP addresses to track their reputation. Microsoft may require verification to confirm IP ownership. Be prepared to provide necessary documentation. Once your request is approved, you’ll gain access to detailed reports that provide valuable insights into your email deliverability status. This will help you monitor and improve your sender reputation over time.

SNDS provides several important metrics that influence your reputation. Understanding these can help you optimize your email strategy.

1. IP & Domain Reputation

Microsoft categorizes your sending reputation into three distinct levels. A green status indicates good standing. This means your emails usually land directly in recipients’ inboxes. When your reputation shifts to yellow, it signals potential issues and some of your emails. You may start being diverted to spam folders. The most serious red status points to poor reputation with a high likelihood of being marked as spam. Your emails may be blocked entirely with this status. If your reputation drops to yellow or red status, it’s important to investigate and address the underlying issues immediately to restore your deliverability.

2. Spam Complaint Rate (SCR)

Microsoft monitors your Spam Complaint Rate (SCR) closely. The SCR measures how frequently recipients mark your email as spam. This metric serves as an indicator of sending reputation, where a high complaint rate raises significant red flags with Microsoft’s filtering systems. Best practices recommend maintaining an SCR below 0.1%. This means no more than 1 complaint per 1,000 emails sent. To achieve this, senders should implement clear and easy ways to unsubscribe while making sure subject lines accurately reflect the content. These measures help maintain trust with both recipients and Microsoft’s email platforms, ultimately supporting better deliverability.

3. Filtered Percentage

This metric shows how many of your emails are being sent to the Junk folder instead of the inbox. A sudden increase suggests deliverability problems.

4. Trap Hits

Microsoft uses spam traps to identify poor list hygiene. Hitting these traps severely damages your reputation. Inbox Rev recommends that you regularly clean your sending lists and remove inactive subscribers.

5. Volume & Traffic Trends

Monitoring your email volume and traffic trends is needed for maintaining good deliverability with Microsoft’s services. Sudden, unexpected spikes in sending volume can raise red flags with spam filters. This can potentially cause your mail to be blocked or diverted to junk folders. It’s important to maintain steady, consistent sending volumes. When you need to scale up your campaigns, the best approach is to implement gradual increases over time. This allows Microsoft’s systems to recognize your sending patterns as legitimate. This measured approach helps establish your reputation as a responsible sender and protects your deliverability rates.

To ensure your emails reach the inbox, follow these proven strategies.

1. Implement Proper Email Authentication

Microsoft prioritizes authenticated emails. Ensure you have:

  • SPF (Sender Policy Framework) – Verifies authorized sending IPs.
  • DKIM (DomainKeys Identified Mail) – Adds a digital signature to prove email integrity.
  • DMARC (Domain-based Message Authentication, Reporting & Conformance) – Tells Microsoft what to do if authentication fails (quarantine or reject).
  • Recommendation: A strict DMARC p=reject policy improves trust with Microsoft.

2. Maintain a Clean Email List

Sending to invalid or inactive addresses hurts your reputation.

  • Use double opt-in to confirm subscriber consent.
  • Remove hard bounces immediately.
  • Regularly prune inactive subscribers (no opens/clicks in 6+ months).

3. Minimize Spam Complaints

High complaint rates lead to filtering.

  • Provide a clear, one-click unsubscribe option.
  • Avoid deceptive subject lines.
  • Segment your lists to send more relevant content.

4. Warm Up New IPs Gradually

New IPs with sudden high volume look suspicious.

  • Start with low volumes.
  • Increase sending gradually (averaging around 4-6 weeks).

5. Monitor SNDS & Test Email Placement

  • Check SNDS daily for reputation changes.
  • Send test emails to Outlook accounts and check if they land in Inbox or Junk.

6. Avoid Spammy Content & Improve Engagement

Low engagement (poor open/click rates) signals spam risk.

  • Personalize emails when possible.
  • Avoid excessive promotional language.

7. Handle Bounces Properly

  • Hard bounces (permanent failures) should be removed.
  • Soft bounces (temporary issues) should be retried, but paused if persistent.

If your SNDS dashboard shows a decline, take these steps:

  1. Pause sending from affected IPs.
  2. Audit your email list for spam traps or inactive users.
  3. Check authentication (SPF, DKIM, DMARC) for errors.
  4. Request a review via Microsoft’s Junk Mail Reporting Program.

SNDS is an extremely important tool for any business sending email to Outlook, Hotmail, or MSN users. You can proactively maintain a strong sender reputation. Following best practices, such as proper authentication, list hygiene, and gradual IP warming, will help you avoid spam filters and maximize inbox placement. By staying vigilant and optimizing your email practices, you can create the best opportunity for reliable deliverability across Microsoft’s systems.

The Key to Stopping Email Bounces

Kristen Wyatt on March 21, 2025

It’s no secret that email marketing is one of the most powerful tools to connect with your audience, build brand loyalty, and drive sales. But let’s be honest – nothing stings more than spending hours crafting the perfect email, hitting “send,” and later discovering it never reached your subscriber. This is where email bounces come into the picture. Bounces are a major factor in email deliverability. Understanding them can mean the difference between a successful campaign and one that falls flat. In this blog, we’ll explore what email bounces are, why they happen, and how you can effectively manage them to maintain a healthy sending list and improve your deliverability rates.

So – Why do bounces occur? An email bounce (or “bounce”) takes place when your email fails to reach the intended recipient’s inbox. Instead of landing in the inbox, it “bounces” back to you. Think of it as the digital version of a “return to sender” notice on a physical letter. Understanding where bounces come from is key to diagnosing and fixing deliverability issues. Bounces can stem from a variety of sources, ranging from technical problems to user behavior.

Let’s break them down into more detail:

1. Invalid or Nonexistent Email Addresses

One of the most common sources of hard bounces is sending email to addresses that don’t exist. This can happen for several reasons:

  • Typos during sign-up: A subscriber might accidentally type something like “gmaul.com” instead of “gmail.com.”
  • Deactivated accounts: The recipient might have deleted or abandoned their email account.
  • Disposable email addresses: Some users sign up with temporary addresses to access gated content, but these often expire quickly.

Consider using a double opt-in process during sign-up to tackle invalid or mistyped email addresses. This requires users to confirm their email by clicking a verification link. You can also use an email verification tool to catch typos or invalid formats before they’re added to your list. These steps will help keep your list clean and improve deliverability.

2. Domain-Related Issues

The domain (the part of the email address after the “@” symbol) can also cause bounces. Common domain-related problems include:

  • Nonexistent domains: The domain might not exist (example: user@nonexistentdomain.com).
  • Misconfigured DNS settings: The domain’s DNS records might not be set up correctly to receive email.
  • Expired domains: The domain may have expired or been deactivated.

Start by verifying domains during sign-up using an email validation tool. This ensures only legitimate, active domains make it onto your list. Regularly audit your list to remove domains that no longer exist. These steps will help keep your list healthy and reduce bounce rates.

3. Full Mailboxes

A soft bounce often happens when the recipient’s mailbox is full and can’t accept new mail. This is common with free email services like Yahoo or AOL which have storage limits.

In cases where an email cannot be delivered due to a recipient’s inbox being full, there’s little you can do immediately except wait and attempt to resend the email at a later time. If the issue persists, it’s best to remove the address from your list to keep it clean and avoid wasting resources. This approach helps to make sure your email list remains focused on active and reachable recipients.

4. Server Issues

Technical problems on the recipient’s side can also cause bounces. These include:

  • Server downtime: The recipient’s email server might be temporarily offline or undergoing maintenance.
  • Overloaded servers: High traffic or resource limitations can prevent the server from accepting new email.
  • Greylisting: Some servers temporarily reject mail from unknown senders as a spam prevention measure, but they usually accept the email on a later attempt.

For temporary issues, try resending the email after a few hours or days. Most email platforms automatically retry delivery over a set period. If the problem continues, remove the address from your list to maintain list hygiene.

5. Email Size and Content Issues

The size and content of your email can also trigger bounces. Some of the most common reasons include:

  • Large attachments: Campaigns with large attachments (over 10MB) may exceed the recipient’s server limits.
  • Spammy content: Certain keywords, excessive use of images, or poorly formatted HTML can trigger spam filters, causing the email to bounce.
  • Authentication failures: If your email lacks proper authentication (SPF, DKIM, DMARC), it may be rejected by the recipient’s server.

Start by compressing large attachments or replacing them with cloud storage links to reduce the likelihood of your email being flagged or blocked. Steer clear of spam-triggering words and phrases like “free,” “act now,” or “limited time offer,” as these can increase the chances of your content being marked as spam. Finally, confirm that your mail is properly authenticated (using protocols like SPF, DKIM, and DMARC) to verify your domain and enhance trust with email providers. These steps will help your email reach recipients’ inboxes more effectively.

6. Blocked Email

Sometimes, your mail is blocked by the recipient’s server or email provider. This can happen for several reasons:

  • IP/Domain blacklisting: If your sending IP address or domain is on a blacklist, your mail may be blocked.
  • Strict spam filters: Some organizations or email providers have aggressive spam filters that block email from unknown senders.
  • Recipient settings: The recipient may have manually blocked your email address or domain.

To resolve these issues, begin by checking if your IP or domain is listed on a blacklist using tools like MX Toolbox. If you are listed, follow the necessary delisting steps to request more information and address the underlying cause. If you’re sending email from a new domain or server, make sure to warm up your IP address gradually by increasing email volume over time to build a positive sender reputation. And encourage your subscribers to add your address to their contacts or whitelist. This can help confirm your mail consistently lands in their inboxes rather than spam folders. These proactive measures will improve your email deliverability and sender credibility.

7. Inactive or Abandoned Accounts

Over time, people stop using certain email accounts. But they may remain on your list. These accounts can lead to bounces if the provider deactivates them.

It’s important to regularly clean your lists by removing inactive subscribers who no longer engage with your email. Before taking this step, consider sending re-engagement campaigns to inactive users to give them an opportunity to reconnect with your content. If they still don’t respond, it’s best to remove them from your list. This practice improves your email engagement rates and helps to make sure your list remains focused on active and interested recipients that can positively impact your sender reputation and deliverability.

8. Role-Based Email Addresses

Role-based email addresses (for example: “info@company.com,” “support@company.com”) are often monitored by multiple people or automated systems. These addresses are more likely to bounce because:

  • They may not accept email from external senders.
  • They might have stricter spam filters.
  • They could be set up to automatically delete or reject certain types of mail.

Avoid sending marketing campaigns to role-based addresses, such as info@ or support@, unless you’re confident they are relevant and appropriate for your campaign. These addresses are often monitored by multiple people or automated systems. This makes them less likely to engage with your content. Instead, focus on targeting personal email addresses. These contacts tend to yield better engagement rates and provide more meaningful connections with your audience.

9. Seasonal or Temporary Issues

Sometimes, bounces are caused by temporary factors, such as:

  • Holiday auto-replies: Some email servers are configured to reject mail when the recipient is on vacation or has set up an auto-reply.
  • Temporary server rules: During high-traffic periods (for example, BFCM), some servers may temporarily tighten their spam filters.

If an email fails to deliver due to these issues (like having a recipient’s server being overloaded), try resending after a few days once the problem has had a chance to resolve itself.  It’s also important to monitor your bounce rates, especially during peak seasons when email servers often experience higher volumes. If you notice an increase in these bounces, consider adjusting your sending frequency or timing to reduce the strain on servers and improve deliverability.

To minimize bounces and enhance your marketing success, it’s incredibly important to take proactive steps that address the root causes. Start by using a reliable Email Service Provider (ESP) to automatically manage bounce-related issues, like retrying soft bounces and removing hard bounce addresses. Regularly monitor your sender reputation with tools like Google Postmaster or SNDS to catch and resolve potential issues early. Educate your subscribers to update their email addresses if they switch providers, helping your list to stay current. And don’t forget to test your campaigns before sending to check for size, formatting, and spam triggers. By understanding the causes of bounce issues and addressing them proactively, you can improve your email deliverability, reduce bounce rates, and position yourself so that your messages reach the right audience. Remember, a clean and well-maintained email list is the foundation of successful email marketing. So don’t skip the maintenance!