Why are my emails suddenly going to spam in Outlook and Hotmail?
Michael Ko
Co-founder & CEO, Suped
Published 31 Jul 2025
Updated 19 Aug 2025
9 min read
It can be incredibly frustrating when your emails, which previously landed in inboxes without issue, suddenly start going to spam folders, particularly in Outlook and Hotmail. This abrupt shift often indicates a change in how email providers, especially Microsoft's robust filtering systems, perceive your sending practices or domain reputation. Unlike a gradual decline, a sudden drop often points to a specific trigger event or a rapid deterioration in a key deliverability factor.
Email deliverability is a complex ecosystem, and Microsoft's filters for Outlook and Hotmail are particularly sophisticated. They evaluate numerous signals, from sender reputation and authentication to content and recipient engagement. When a sudden change occurs, it's like a warning light has illuminated, signaling that something significant has shifted on your sending side.
Identifying the root cause quickly is crucial to restoring your email deliverability. This often involves a systematic investigation into recent changes in your email campaigns, infrastructure, or recipient behavior. Understanding these potential triggers is the first step towards getting your legitimate emails back into the inbox.
Sender reputation and engagement
One of the most common reasons for a sudden drop in deliverability is a hit to your sender reputation. Email providers meticulously track how recipients interact with your emails. If there's a sudden increase in complaints or a decrease in positive engagement, it can trigger filters to send your mail directly to the junk folder.
A sudden spike in unsubscribe requests or, more critically, a surge in spam complaints, can severely damage your reputation. Even a small percentage of complaints can have a disproportionately large impact, as email providers prioritize user experience and aggressively filter what they deem to be unwanted mail. This is why understanding your engagement metrics is essential.
Another factor is sending inconsistent email volumes or dramatically changing your sending patterns. Email providers prefer consistent, predictable sending behavior. Sudden increases in volume or sending to entirely new segments can flag your emails as suspicious, even if they are legitimate. This triggers their filters to scrutinize your mail more closely.
Poor list hygiene is a frequent culprit. If you've recently sent to an old, unengaged list, or one containing a significant number of inactive addresses, you might hit spam traps (also known as honeypots). Hitting these traps immediately signals to email providers that your list acquisition or maintenance practices are problematic, leading to severe penalties like blacklisting (or blocklisting) and junk folder placement.
Monitor Engagement: Keep a close eye on your open rates, click-through rates, and, most importantly, spam complaint rates within your email service provider's analytics and Microsoft's Sender Support Portal.
Segment and Target: Send relevant content to engaged subscribers to minimize complaints.
Maintain List Hygiene: Regularly clean your email list to remove inactive or bouncing addresses and avoid spam traps.
Technical configuration and blocklists
Technical misconfigurations or issues with your email authentication can also cause an immediate drop in deliverability. This is especially true for crucial protocols like SPF, DKIM, and DMARC. A sudden change in your DNS records, or an issue with your email service provider, can break these authentication methods.
If your SPF record (Sender Policy Framework) is misconfigured, it signals to receiving mail servers that your emails might not be authorized. Similarly, issues with DKIM (DomainKeys Identified Mail) signatures can lead to authentication failures. Outlook and Hotmail are particularly strict with these authentication checks, and a failure can result in immediate junking of your messages. Microsoft's own Office 365 Message Analyzer can help diagnose header issues.
Being placed on an email blocklist (or blacklist) can instantly tank your deliverability. If your sending IP address or domain recently appeared on a major public or private blocklist, it will cause your emails to be rejected or sent to spam. This often happens due to a sudden surge in spam complaints, sending to spam traps, or even a compromised email account.
Microsoft maintains its own internal blocklists and uses data from various sources to determine if an IP or domain should be blocked. Even if you're not on a public blacklist, Microsoft's SmartScreen filter might privately blocklist (or blacklist) your sender. For Office 365 users, this can be particularly impactful.
Before the issue
Email authentication (SPF, DKIM, DMARC) records were correctly configured and stable. Sender IP and domain were not listed on any major public blocklists. Consistent sending volume and frequency with gradual list growth. User engagement (opens, clicks) was healthy, and complaint rates were low.
After the issue
A recent change to DNS records or email service provider introduced authentication failures. IP or domain suddenly appeared on a blocklist after sending to old or purchased lists. Abrupt increase in email volume or sending to unsegmented audiences. Sharp increase in spam complaints or decrease in engagement.
To troubleshoot this, you need to verify your SPF, DKIM, and DMARC records immediately. Use a free online email testing tool to check if your DNS records are correctly set up and if emails are passing authentication checks. If they fail, that's a major red flag.
How to check your SPF record
An SPF record is a TXT record in your DNS that specifies which mail servers are authorized to send emails on behalf of your domain. A typical SPF record looks like this:
If you've recently changed email service providers or added a new sending platform, your SPF record might be outdated or incomplete, causing authentication failures. This is a common issue when sending from Gmail SMTP or other third-party services.
Content and recipient engagement
Even if your technical setup is perfect, your email content can trigger spam filters. Sudden changes to your email copy, subject lines, or even the layout can make your emails look suspicious to Microsoft's sophisticated SmartScreen filters.
Using excessive capitalization, exclamation marks, or spam trigger words (e.g., 'free money,' 'winner,' 'urgent') can instantly flag your emails. Similarly, poorly formatted HTML, broken links, or an unusual ratio of images to text can also be red flags. I’ve found that even seemingly minor changes can impact how your emails are perceived. For newsletter senders, this is a common issue, and we have a specific guide on why newsletters land in spam.
Even if your content and authentication are good, a sudden drop in user engagement can cause your emails to go to spam. If recipients suddenly stop opening, clicking, or start deleting your emails without reading them, this sends a negative signal to Hotmail and Outlook filters. They interpret this as a lack of interest, or worse, that your emails are unwanted.
A common scenario is when a campaign goes out and receives an unexpectedly high number of 'this is junk' reports directly from recipients. These direct reports carry significant weight with email providers and can quickly impact your sender reputation, causing subsequent emails to be flagged as spam. This also explains why emails go to junk even with strong technical setup.
Immediate troubleshooting steps
When emails suddenly start landing in spam or junk folders, it requires swift action. The first step is always to verify your domain and IP reputation using blocklist monitoring tools. If you find your domain or IP on a major blocklist, initiate the delisting process immediately and address the underlying cause.
Next, meticulously check your email authentication records, especially SPF, DKIM, and DMARC. Even a small syntax error or an outdated IP address in your SPF record can cause authentication failures, leading to spam placement. Ensure your DMARC policy is correctly configured to monitor and enforce your sending practices effectively. I often recommend DMARC monitoring for proactive insights.
If technical issues are ruled out, focus on your content and audience engagement. Review recent email campaigns for any changes in messaging, subject lines, or call-to-actions that might appear spammy. Segment your audience and send smaller batches to highly engaged users first to rebuild your reputation. Actively encourage recipients to add you to their safe senders list and move emails from junk to inbox.
Lastly, engage with Microsoft's Sender Support for Outlook.com (SNDS) and Junk Mail Reporting Program (JMRP). These tools provide valuable insights into your sending reputation and complaint rates specifically from Microsoft users. Sometimes, direct engagement with their support team can lead to a quicker resolution. We have a dedicated guide on how to prevent emails from going to spam in Outlook and Hotmail that provides a comprehensive checklist.
Factor
Impact
Action
Spam complaints
Directly impacts sender reputation. High complaint rates lead to immediate junking.
Sending to invalid or old addresses. Instant bad reputation.
Clean your list, use double opt-in.
Content issues
Spammy words, poor formatting, broken links.
Review content, avoid trigger words, test email rendering.
Views from the trenches
Best practices
Segment your audience based on engagement levels to improve relevancy and reduce complaints.
Regularly clean your email lists by removing inactive or bouncing addresses.
Implement a double opt-in process for all new subscribers to ensure high-quality leads.
Common pitfalls
Sending to purchased or old, unengaged email lists, increasing the risk of spam trap hits.
Making sudden, drastic changes to email volume or sending frequency without warming up.
Ignoring authentication failures (SPF, DKIM, DMARC) or not monitoring their status.
Expert tips
Use a dedicated IP address for high-volume sending to isolate your reputation from others.
Implement BIMI to display your brand logo and increase trust with recipients.
Regularly test your email deliverability across various email providers, not just Microsoft.
Marketer view
Marketer from Email Geeks says a sudden shift to spam in Outlook/Hotmail often points to a recent change in how Microsoft's filters perceive your emails, perhaps due to changed sending behavior or content.
2020-05-06 - Email Geeks
Expert view
Expert from Email Geeks says checking engagement at Microsoft-managed domains (Outlook, Hotmail, MSN) is a good starting point to see if your deliverability has gone down recently, as they measure by engagement and spam complaints versus send volume.
2020-05-06 - Email Geeks
Restoring your inbox placement
A sudden shift of your emails to the spam folder in Outlook and Hotmail is a clear indication that something significant has changed. Whether it's a dip in sender reputation, an authentication issue, a blocklist placement (or blacklist hit), or content-related flags, immediate investigation and remediation are essential. Proactive monitoring of your email metrics and consistent adherence to best practices are key to maintaining good deliverability and avoiding future issues.
By systematically checking your authentication records, monitoring your sender reputation, analyzing content, and maintaining clean lists, you can identify and resolve the problem. Remember, email deliverability is an ongoing effort, and staying vigilant is your best defense against the junk folder.
