How to prevent emails from going to spam in Microsoft Hotmail or Outlook?
Matthew Whittaker
Co-founder & CTO, Suped
Published 5 Aug 2025
Updated 19 Aug 2025
5 min read
Getting your emails into the inbox of Microsoft Hotmail and Outlook.com recipients can be a significant challenge for email marketers and businesses. Their filtering systems are among the most stringent, often diverting even legitimate messages into the junk or spam folder. This can severely impact your engagement rates and the effectiveness of your email campaigns.
Many senders find themselves in a frustrating loop where their emails are constantly marked as spam, even when all traditional deliverability checks, like proper authentication and good reputation scores, seem to pass. This issue isn't uncommon and often stems from a deeper understanding of how Microsoft (formerly Hotmail) evaluates incoming mail.
To ensure your emails consistently reach the inbox, you need to go beyond basic setup. It involves a holistic approach encompassing technical configurations, content optimization, and proactive engagement strategies. Let's explore the key factors that influence deliverability to these demanding inboxes.
How Microsoft Hotmail and Outlook filter emails
Microsoft’s spam filters, particularly for Hotmail and Outlook, utilize a sophisticated blend of factors to determine whether an email is legitimate or junk. It's not just about standard authentication protocols. Their system weighs heavily on sender reputation, engagement metrics, and even specific content characteristics.
One crucial element is the Spam Confidence Level (SCL) which is assigned to each incoming message. An SCL score above a certain threshold (often 2 or 3) can automatically route emails to the junk folder. This score is influenced by various elements within your email, including subject lines, text, images, and overall layout.
Sender reputation: This is paramount. Microsoft tracks your sending behavior, including complaint rates, bounce rates, and whether your IP or domain is on any significant blocklists (or blacklists).
User engagement: How users interact with your emails is critical. Opens, clicks, and especially moving an email from junk to inbox or adding you to the safe sender list signals trustworthiness. Conversely, marking emails as junk or deleting them without opening harms your reputation.
Content analysis: Beyond spam trigger words, Microsoft's filters analyze the overall content for suspicious patterns, disproportionate image-to-text ratios, and hidden text.
Laying the foundation with email authentication
Robust email authentication is the bedrock of good deliverability. Even with Microsoft's complex filtering, proper SPF, DKIM, and DMARC setup verifies your identity as a legitimate sender. This tells email providers that your emails haven't been forged or tampered with.
The authentication trio
SPF (Sender Policy Framework): Authorizes specific servers to send email on behalf of your domain. A missing or improperly configured SPF record can lead to emails failing authentication checks.
DKIM (DomainKeys Identified Mail): Adds a digital signature to your emails, allowing recipients to verify that the message hasn't been altered in transit and truly originated from your domain. Ensure your DKIM selector name examples are correctly set up.
DMARC (Domain-based Message Authentication, Reporting & Conformance): Builds upon SPF and DKIM, telling receiving servers how to handle emails that fail authentication (e.g., quarantine or reject) and provides valuable DMARC reports. Implement a DMARC policy to enforce your authentication.
For Microsoft's new sender requirements in 2024, DMARC is becoming increasingly mandatory for bulk senders. If your emails are still hitting the junk folder, double-check your DMARC records and ensure they are aligned with your sending practices.
Optimising content and engagement
Even with perfect authentication, poor content or engagement can lead to your emails being flagged as spam. Microsoft's filters are highly sensitive to user behavior and perceived content quality.
Content best practices
Image-to-text ratio: Aim for a balanced ratio. Too many images and too little text can trigger spam filters, especially if those images contain hidden text or call-to-actions.
Clear subject lines: Avoid misleading or overly promotional language that might seem spammy. Be direct and relevant to the email's content.
Personalization: Personalize emails where appropriate. Generic, mass-sent emails are more likely to be filtered.
Plain text version: Always include a plain text version of your email. This improves accessibility and helps avoid spam triggers.
Engagement strategies
Segment lists: Send to your most engaged subscribers. High engagement signals trustworthiness to Microsoft's filters.
Encourage whitelisting: Ask recipients to add your email address to their safe sender list or contacts. This is a powerful signal.
Monitor spam complaints: Keep complaint rates low by immediately removing users who mark your emails as spam.
Double opt-in: Implement double opt-in to ensure subscribers genuinely want your emails, reducing complaints and improving engagement.
Continuously test your email content and layout. Sometimes minor adjustments to the structure or wording can significantly impact your Spam Confidence Level within Microsoft systems, helping to avoid the junk folder.
Continuous monitoring and troubleshooting
Even with the best practices in place, issues can arise. Consistent monitoring of your email performance and proactive troubleshooting are essential, especially when dealing with Microsoft's filters, which can be particularly opaque.
Using Microsoft's sender support programs
Junk Mail Reporting Program (JMRP): Provides feedback on spam complaints from Hotmail and Outlook users. This is invaluable for identifying and removing problematic subscribers quickly.
Smart Network Data Services (SNDS): Offers insights into your IP reputation, spam trap hits, and other key metrics as seen by Microsoft. Regular checking of SNDS can help you spot issues before they escalate.
If your emails are still consistently going to spam, despite good scores on JMRP and SNDS, you might be facing an internal reputation issue that is harder to diagnose. In such cases, carefully analyze email headers for any clues regarding the Spam Confidence Level (SCL) or other diagnostic information that Microsoft might embed. Sometimes, a blocklist (or blacklist) listing could be the culprit, even if it's not immediately apparent.
Views from the trenches
Best practices
Actively encourage subscribers to add your email address to their safe senders list in Hotmail/Outlook, as this provides a strong positive signal.
Regularly clean your email lists by removing inactive or unengaged subscribers to improve overall sending reputation and reduce bounce rates.
Use Microsoft's Junk Mail Reporting Program (JMRP) and Smart Network Data Services (SNDS) to monitor feedback and IP reputation, enabling proactive issue resolution.
Adjust the image-to-text ratio within your email content to ensure it appears balanced and avoids triggering Hotmail's spam filters.
Implement a double opt-in process for all new subscribers to confirm their genuine interest and reduce the likelihood of spam complaints.
Common pitfalls
Ignoring the Spam Confidence Level (SCL) header in email, which indicates how likely Microsoft's filters consider your email to be spam.
Failing to adequately segment your email lists, resulting in sending to disengaged users who are more likely to mark your emails as junk.
Relying solely on external blocklist checkers, as Microsoft often uses internal, private blocklists (or blacklists) that aren't publicly visible.
Using overly promotional or keyword-stuffed subject lines and content that triggers Microsoft's aggressive spam detection algorithms.
Not having robust email authentication (SPF, DKIM, DMARC) properly configured, leading to emails failing basic sender verification checks.
Expert tips
Sometimes, even with good SNDS scores, a specific campaign's content or layout can have a high SCL, causing it to land in spam.
Be mindful of any corporate domains in your client database, as a high number of spam complaints from these recipients can negatively impact your overall Hotmail deliverability.
When troubleshooting, focus on tweaking small elements like subject lines and content layout, then retest to see if the SCL improves.
It's crucial to decode the 'x-message-delivery' header for the true SCL value, as it can be hidden in Base64 encoding.
Don't rely on templated support responses; instead, use data from JMRP and SNDS to pinpoint specific issues Microsoft may be seeing.
Marketer view
Marketer from Email Geeks says they have a client with correct authentication and good JMRP and SNDS reputation, but emails are still consistently moved to the junk folder by Microsoft Hotmail and Outlook. Open rates for these domains are significantly lower.
April 26, 2019 - Email Geeks
Expert view
Expert from Email Geeks says to check the spam score of the content assigned by Hotmail, which is available in the email headers. Content with a score greater than 2 often lands in spam, so adjusting image-to-text ratio, subject lines, and content layout can help improve inboxing.
April 27, 2019 - Email Geeks
Key takeaways for Hotmail and Outlook deliverability
Achieving consistent inbox placement with Microsoft Hotmail and Outlook requires more than just meeting basic technical standards. It demands a proactive and comprehensive approach that addresses authentication, sender reputation, content quality, and recipient engagement.
By meticulously configuring your email authentication protocols (SPF, DKIM, DMARC), carefully crafting your email content to avoid spam triggers, and continuously monitoring your sender reputation through tools like JMRP and SNDS, you significantly increase your chances of bypassing the junk folder. Remember, user engagement is a powerful signal to Microsoft's filters, so foster positive interactions and clean your lists regularly.
Staying informed about Microsoft's new sender requirements and continuously optimizing your strategy will help ensure your messages land where they belong: in the inbox.
Getting your emails into the inbox of Microsoft Hotmail and 
Outlook.com recipients can be a significant challenge for email marketers and businesses. Their filtering systems are among the most stringent, often diverting even legitimate messages into the junk or spam folder. This can severely impact your engagement rates and the effectiveness of your email campaigns.
Microsoft (formerly Hotmail) evaluates incoming mail.
