How can I improve email deliverability with Microsoft and avoid spam filters?
Matthew Whittaker
Co-founder & CTO, Suped
Published 9 May 2025
Updated 16 Aug 2025
7 min read
Navigating the complexities of email deliverability, especially when sending to Microsoft services like Outlook and Hotmail, can often feel like an uphill battle. It is a common source of frustration for many senders, with emails sometimes ending up in the junk folder despite best efforts. I've heard countless stories, and experienced firsthand, how challenging it can be to get consistent inbox placement.
The good news is that with a strategic approach, a clear understanding of their filtering mechanisms, and adherence to established best practices, you can significantly improve your email deliverability and avoid spam filters. This guide will help you understand what it takes to land in the inbox of Microsoft users.
Understanding Microsoft's filtering approach
Microsoft employs a multi-layered approach to protect its users from unwanted email, utilizing a combination of connection filtering, content filtering, and advanced machine learning algorithms. Their systems analyze various elements of an incoming email, from the sender's IP and domain reputation to the message content itself, to determine whether it is legitimate or potential spam (also known as a blocklist hit). It is important to note that you cannot completely disable spam filtering within Microsoft 365, so focusing on deliverability best practices is crucial.
A key factor in Microsoft's assessment is your sender reputation. This reputation is built over time based on your sending habits, recipient engagement, and how often your emails are marked as spam. A positive reputation signals to Microsoft that you are a trustworthy sender, increasing the likelihood of your emails reaching the inbox. Conversely, a poor reputation can quickly lead to emails being quarantined or sent directly to the junk folder, and even result in your IP address or domain being added to a blacklist.
Understanding these underlying mechanisms is the first step towards improving your email deliverability. For a more detailed look at how their anti-spam policies function, you can consult Microsoft's own documentation on anti-spam policies.
Foundation of trust: email authentication
Email authentication protocols are the cornerstone of establishing trust with Microsoft's mail servers. SPF, DKIM, and DMARC tell receiving servers that your emails are legitimate and prevent spoofing. Microsoft places significant emphasis on these standards, especially with their new sender requirements. Ensure these are correctly configured for your sending domains.
SPF: Sender policy framework
This DNS TXT record specifies which mail servers are authorized to send email on behalf of your domain. A common issue I've seen is an SPF record that is technically passing but incorrectly set up for your sending infrastructure. Proper configuration is vital, and it directly impacts your open rates. An example of a simple SPF record looks like this:
Example SPF recordDNS
v=spf1 include:_spf.example.com ~all
For DKIM, your outgoing emails should be digitally signed. This signature allows the receiving server to verify that the email has not been tampered with in transit. Incorrectly configured DKIM can lead to authentication failures, which are red flags for Microsoft's spam filters. Always ensure your DKIM keys are valid and published correctly in your DNS. You can learn more about DKIM errors and how to troubleshoot them.
Finally, DMARC builds on SPF and DKIM, providing a framework for domain owners to specify how receiving servers should handle emails that fail authentication. This protocol is becoming increasingly important, with major providers like Microsoft making it a requirement for bulk senders. Implementing DMARC allows you to receive reports on your email traffic, providing invaluable insights into potential spoofing attempts and authentication issues. A basic guide to DMARC, SPF, and DKIM can help you understand the foundational elements.
Content and engagement best practices
Beyond technical configurations, the content of your emails and how recipients interact with them play a significant role in deliverability. Microsoft's filters analyze various elements within your message to assess its legitimacy. This includes everything from the subject line and body text to the types of links and images included.
Content to avoid
Spammy keywords: Overuse of promotional language, excessive exclamation points, or all caps.
Misleading subject lines: False promises or unrelated topics to trick recipients into opening.
Shortened or broken URLs: These can appear suspicious to filters. Use full, clean links.
Too many images or large attachments: Can flag your email. Balance text and visuals.
Content to embrace
Clear, concise subject lines: Directly reflect the email's content.
Personalization: Tailor content to the recipient's needs and preferences.
Value-driven content: Provide helpful information rather than just sales pitches.
Plain text option: Ensure a well-formatted plain text version exists for accessibility and deliverability.
Recipient engagement is paramount. Microsoft, like other major mailbox providers, closely monitors how users interact with your emails. High open rates, clicks, and positive interactions (e.g., moving emails out of junk, adding to contacts) boost your reputation. Conversely, low engagement, high spam complaints, or frequent deletions without opening can negatively impact your standing and lead to emails being filtered. Maintaining a clean and engaged email list is one of the most effective strategies to improve deliverability to Microsoft services. You can also refer to our guide on how to effectively avoid spam filters.
Managing your sending reputation and troubleshooting
Your sending reputation is a holistic score that Microsoft assigns to your domain and IP address. It is dynamic and influenced by a variety of factors, including bounce rates, spam complaint rates, and how recipients engage with your emails. High bounce rates, especially hard bounces (permanent delivery failures), signal to Microsoft that your list quality is poor. Similarly, a surge in spam complaints, even from a small percentage of recipients, can severely damage your reputation and lead to your emails being directed to the junk folder or even result in your domain or IP being placed on a blocklist.
When starting with a new IP address or warming up an old one, a gradual approach is essential. Sending large volumes of emails from a cold IP can immediately trigger spam filters. Start with small volumes and slowly increase them over time, monitoring your deliverability closely. If you encounter deliverability issues or your emails start going to spam, don't panic. You can often troubleshoot and resolve Outlook email deliverability issues by systematically checking your configurations and sender reputation.
If you find your emails consistently hitting the junk folder, especially during a warmup period, consider reaching out to Microsoft support. Some senders have had success requesting "preemptive accommodation", providing details about your sending IPs, dates, and estimated volumes. While it can sometimes feel like a roll of the dice, persistence with tickets can lead to Microsoft adjusting their filtering for your traffic. Regularly monitoring your IP and domain status on various blocklists (or blacklists) is also crucial, as a listing can severely impede your deliverability. You can use a blocklist checker to keep an eye on your status.
Views from the trenches
Best practices
Maintain a clean email list by regularly removing inactive or invalid addresses to reduce bounce rates and spam complaints.
Implement a double opt-in process to ensure all subscribers genuinely want to receive your emails, improving engagement.
Consistently monitor your email deliverability metrics, including open rates, click-through rates, and spam complaint rates.
Prioritize personalized and valuable content over overly promotional or generic messages to foster recipient engagement.
Ensure all email authentication records (SPF, DKIM, DMARC) are correctly configured and monitored for compliance.
Common pitfalls
Sending large volumes of email from a new or cold IP address without a proper warmup strategy, triggering spam filters.
Using misleading subject lines or excessive spammy keywords that can immediately flag your emails as suspicious.
Ignoring DMARC reports, missing critical insights into email authentication failures and potential spoofing attempts.
Failing to respond persistently to Microsoft support tickets when experiencing deliverability issues, expecting quick fixes.
Not maintaining list hygiene, leading to high bounce rates and spam trap hits that damage sender reputation.
Expert tips
When initiating a new email sending campaign or warming up an IP, open a proactive ticket with Microsoft support.
Provide Microsoft support with your sending IP ranges, expected volumes, and anticipated dates for better accommodation.
Be patient and persistent with Microsoft support tickets, even if initial responses are automated or seem unhelpful.
Always include valid, clean URLs in your email content, avoiding any form of URL shortening that could be flagged.
Consider segmenting your audience and tailoring content to improve engagement, which positively impacts deliverability.
Marketer view
Marketer from Email Geeks says: I've been working on a case where emails mysteriously disappear from the inbox and reappear in the spam folder, even after showing a 'DEST:I' in the headers, it's quite frustrating.
2022-07-20 - Email Geeks
Expert view
Expert from Email Geeks says: When starting a warmup, open a ticket with Microsoft and ask for 'preemptive accommodation'. They usually respond requesting IPs, dates, and estimated volumes, then adjust their filtering.
2022-07-20 - Email Geeks
Achieving consistent inbox placement
Improving email deliverability with Microsoft is not a one-time fix, but an ongoing commitment to best practices. It requires a solid foundation of email authentication, careful attention to your content and recipient engagement, and proactive management of your sender reputation. While Microsoft's filtering can be stringent, consistent effort and a clear understanding of their expectations will pave the way for better inbox placement.
By focusing on these areas, monitoring your performance, and being prepared to engage with Microsoft support when necessary, you can significantly reduce the chances of your emails ending up in the spam folder and ensure your messages reach their intended audience. Remember that consistent, wanted mail from an authenticated sender is always the goal. Our comprehensive guide on why your emails are going to spam can provide further insights.
services like Outlook and Hotmail, can often feel like an uphill battle. It is a common source of frustration for many senders, with emails sometimes ending up in the junk folder despite best efforts. I've heard countless stories, and experienced firsthand, how challenging it can be to get consistent inbox placement. 
