How to improve email deliverability to Outlook.com and Microsoft email services?
Michael Ko
Co-founder & CEO, Suped
Published 17 Jul 2025
Updated 15 Aug 2025
7 min read
Getting your emails consistently delivered to Outlook.com and other Microsoft email services can be a significant challenge for even the most experienced senders. Unlike some other mailbox providers, Microsoft's filtering systems are notoriously strict, often junking emails instantly without clear indications in the headers of why the delivery failed. This can be frustrating, especially when your sender reputation seems clean on other platforms and your authentication records are correctly set up.
Many email marketers and businesses encounter deliverability issues with Microsoft, including Hotmail and Live.com domains. It is important to understand that Microsoft uses a multi-layered approach to email filtering, combining technical compliance with sender reputation and user engagement metrics. Merely having your SPF, DKIM, and DMARC records in place might not be enough if other factors are flagging your emails.
This guide will walk you through the critical steps and best practices to improve your email deliverability to Outlook.com and other Microsoft services, helping you bypass the junk folder and reach the inbox reliably.
Establish strong email authentication
Email authentication protocols like SPF, DKIM, and DMARC are fundamental for proving your legitimacy as a sender. Microsoft, like other major mailbox providers, relies heavily on these records to verify that your emails are truly from your domain and haven't been tampered with. Proper configuration is the first and most crucial step in ensuring your emails are not immediately flagged as suspicious or spam.
SPF (Sender Policy Framework) allows you to specify which mail servers are authorized to send email on behalf of your domain. DKIM (DomainKeys Identified Mail) provides a way for senders to digitally sign outgoing emails, allowing recipients to verify that the email was sent by the domain owner and has not been altered in transit. Both are essential for establishing trust.
DMARC (Domain-based Message Authentication, Reporting, and Conformance) builds upon SPF and DKIM by allowing you to tell receiving mail servers what to do with emails that fail authentication and provides aggregated reports on your email sending. Implementing a DMARC policy that moves towards a quarantine or reject state is crucial for Microsoft's trust in your domain. We have seen many email deliverability problems with Outlook.com stem from DMARC issues.
DNS records for email authentication
For SPF, you add a TXT record to your DNS that lists authorized sending IPs and domains. For DKIM, you'll publish a public key as a TXT record. DMARC requires a TXT record that defines your policy and reporting preferences.
Your sender reputation is paramount for deliverability to Microsoft services. This reputation is built over time based on factors such as spam complaints, bounce rates, spam trap hits, and user engagement. Microsoft's filters are particularly sensitive to these signals. A sudden spike in negative metrics can quickly land your emails in the junk folder, even if your technical setup is perfect.
When sending from new IPs or domains, proper IP warming is critical. Start with low volumes and gradually increase them over several weeks. This helps Microsoft (and other ISPs) recognize your sending patterns as legitimate, building a positive reputation rather than triggering spam filters due to an uncharacteristic volume.
Maintaining a clean and engaged email list is perhaps the most impactful factor. Microsoft aggressively filters emails sent to unengaged users or spam traps. Regularly remove inactive subscribers who haven't opened or clicked your emails in a long time. Implement double opt-in to ensure subscribers genuinely want your emails, reducing spam complaints and improving overall engagement.
Engaged lists
Segment audience: Send to subscribers who have opened or clicked within the last 30-90 days.
Confirm consent: Use double opt-in to verify subscriber intent and reduce spam complaints.
Remove inactives: Regularly scrub your list of non-engaging or bouncing addresses.
Unengaged lists
Broad audience: Mailing to an entire list without considering recent activity.
Single opt-in: Higher risk of spam traps and invalid addresses leading to bounces.
Ignoring metrics: Continuing to send to users with zero opens or clicks for months.
Consistent sending volume and frequency are also important. Erratic sending patterns can negatively impact your reputation with Microsoft, as it may appear suspicious. Stick to a predictable schedule and volume that aligns with your usual sending habits.
Optimize email content and structure
Beyond technical authentication and sender reputation, the content and technical structure of your emails play a significant role in deliverability. Microsoft's spam filters analyze email content for characteristics commonly associated with spam, such as excessive images, suspicious links, and keyword stuffing.
Ensure your email content is relevant, engaging, and provides clear value to the recipient. Avoid using too many images relative to text, as this can often be a red flag. All links within your email should be valid, functional, and point to reputable domains. Broken or suspicious links can severely damage your deliverability.
Consider sending plain text versions alongside your HTML emails. While HTML offers rich formatting, a plain text alternative ensures your message is accessible and can sometimes help with deliverability, especially if your HTML is complex or poorly coded. Keep email sizes reasonable, typically under 25 MB, to avoid throttling or rejection.
Monitor and troubleshoot deliverability
Even with perfect authentication and a stellar reputation, issues can arise. Proactive monitoring and knowing how to troubleshoot are essential. Microsoft provides tools to help senders understand their reputation and resolve deliverability problems. One primary tool is Smart Network Data Services (SNDS).
SNDS provides data on your IP's health, including email volume, complaint rates, and spam trap hits. Registering your sending IPs in SNDS (Smart Network Data Services) and participating in the Junk Mail Reporting Program (JMRP) are crucial steps. JMRP sends you copies of emails that Outlook.com users mark as junk, giving you direct feedback to clean your list and refine content.
If your IP address or domain is placed on a blocklist (or blacklist), you might need to submit a delisting request directly to Microsoft. Be prepared to provide detailed information about your sending practices and what steps you've taken to resolve the underlying issues. Remember that Microsoft's support process can sometimes take time, and consistent adherence to best practices is the best long-term solution. You can also monitor your blocklist status using a blocklist checker.
If you're facing ongoing issues, a period of reduced or paused sending to Microsoft domains can sometimes help reset your reputation. During this time, focus on re-engaging your audience, cleaning your list, and ensuring all technical configurations are impeccable.
Views from the trenches
Best practices
Maintain a hyper-engaged list, focusing on active subscribers who regularly open and click your emails to Microsoft domains.
Consistently monitor your sender reputation using Microsoft's Smart Network Data Services (SNDS) and the Junk Mail Reporting Program (JMRP).
Ensure all email authentication protocols (SPF, DKIM, DMARC) are correctly configured and aligned, moving towards a reject policy for DMARC.
Common pitfalls
Sending to unengaged or inactive users, which significantly hurts your sender reputation and triggers spam filters.
Ignoring spam complaints or bounce notifications, preventing you from identifying and addressing underlying issues.
Failing to implement or properly configure DMARC, leaving your domain vulnerable to spoofing and reducing trust with Microsoft.
Expert tips
Microsoft's filters are among the strictest, so what might pass elsewhere won't necessarily pass here.
A complete rebuild of domain reputation, including a temporary pause in sending and a gradual warm-up, can be highly effective.
Don't expect special treatment from Microsoft support outside their designated processes; focus on fixing your own practices.
Expert view
Expert from Email Geeks says Microsoft has layers of policy and autoresponders, so consider a total rebuild of your domain reputation by pausing mailing and gradually increasing volumes, especially targeting engaged users.
January 19, 2021 - Email Geeks
Expert view
Expert from Email Geeks says that Microsoft's lawyers prohibit direct interaction outside the designated process, meaning special treatment for specific cases is unlikely.
January 20, 2021 - Email Geeks
Final thoughts on Outlook deliverability
Improving email deliverability to Outlook.com and other Microsoft email services requires a comprehensive approach. It's not just about setting up SPF, DKIM, and DMARC, though these are critical foundations. It's equally about meticulously managing your sender reputation, ensuring genuine user engagement, and adhering to content best practices.
By proactively monitoring your sender metrics via Microsoft's tools, keeping your email list clean and engaged, and understanding their strict filtering policies, you can significantly enhance your chances of landing in the inbox rather than the junk folder. Consistency and continuous optimization are key to long-term success with Microsoft domains.
Outlook.com and other 
Microsoft email services can be a significant challenge for even the most experienced senders. Unlike some other mailbox providers, Microsoft's filtering systems are notoriously strict, often junking emails instantly without clear indications in the headers of why the delivery failed. This can be frustrating, especially when your sender reputation seems clean on other platforms and your authentication records are correctly set up.
