Microsoft 365 uses advanced spam filters to protect inboxes from unwanted emails. If you're involved in email outreach, understanding these filters is essential to ensure your messages land in the inbox. Here's what you need to know:
By addressing both content and technical factors, you can improve your email deliverability and avoid spam filters.
Understanding the content factors that prompt Microsoft 365 to flag emails as spam is crucial for ensuring your messages land in the inbox.
Microsoft 365's spam filters are designed to spot words and phrases that come across as overly promotional, deceptive, or fraudulent. With 160 billion spam emails circulating daily and 46.8% of all emails in December 2023 classified as spam, these filters have become highly adept at identifying problematic language.
The system doesn’t just scan the main text - it evaluates every component of your email, including subject lines, body content, headers, hyperlinks, image alt text, footers, HTML, CSS, and even attachment names. A single questionable phrase in any of these areas can hurt deliverability.
| Category | Example Spam Words |
|---|---|
| Money & Financial | 100% free, Earn cash, Make money fast |
| Scam & Fraud | Risk-free, Guaranteed winner, No catch |
| Marketing & Overpromises | Act now, Limited-time offer, Buy direct |
| Urgency & Pressure | Only 24 hours left, Urgent response needed |
| Health & Pharma | Miracle cure, Anti-aging formula, No prescription needed |
Context is key when using these words. As Yaroslav, a Deliverability Expert at Mailtrap, explains:
"Spam filters nowadays are beginning to pay more attention not just to specific spam words as might have been the case previously but also to the overall reputation of the sender and the engagement generated by email recipients."
To avoid issues, use these terms sparingly and ensure your email is well-coded. Maintaining a strong sender reputation and generating positive engagement can also help. However, with nearly one in five emails being flagged by spam filters, it’s wise to tread carefully.
Beyond word choice, the design and coding of your email also influence spam scores.
Email layout is another critical factor in deliverability. Poor formatting often raises red flags for Microsoft 365's spam detection system. For instance, excessive capitalization, punctuation, and spammy phrases in subject lines are immediate triggers. Formatting issues like these are often interpreted as signs of unprofessionalism.
Other common pitfalls include mixed fonts, large blocks of text, and overly complex HTML code. A cluttered or disorganized email layout not only hurts readability but also increases the likelihood of being flagged by spam filters. Clean, straightforward formatting improves both user experience and deliverability.
Responsive design is equally important. Emails that don’t display correctly on mobile devices or have broken formatting elements are more likely to be marked as spam. Since Microsoft 365 processes emails across a variety of devices, ensuring consistent formatting across all screen sizes is essential.
Even your email signature can pose a risk. Signatures overloaded with links or images can trigger spam filters. To minimize this risk, keep your signature concise - 1 to 3 essential links - and use text links instead of image-based ones.
The balance between images, links, and text in your email also plays a vital role in whether it reaches the inbox. Microsoft 365's filters pay close attention to this ratio. Emails with too many images compared to text are often flagged as spam. A 60:40 text-to-image ratio is recommended for optimal results.
Similarly, an excessive number of links can increase the chances of your email being classified as spam. Aim for a link-to-text ratio of no more than 1 link per 100 words, and ensure all links direct to reputable websites.
Large images can also cause problems, as spam filters may struggle to analyze the text content within them. To avoid this, use HTML text instead of embedding text in images, and compress images while adding descriptive alt text to maintain the recommended 60:40 ratio.
For businesses managing multiple mailboxes, tools like Primeforge can help enforce these content standards, boosting sender reputation. Paying attention to these details lays a solid foundation for tackling the technical aspects of email setup.
Technical missteps can be just as damaging as content issues when it comes to email deliverability. These misconfigurations often serve as the foundation for deeper problems, making it crucial to address them early.
Email authentication protocols act as your digital ID, proving to Microsoft 365 that you're a legitimate sender. Without proper setup for SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-Based Message Authentication, Reporting and Conformance), your emails are at risk of being flagged as spam - or worse, blocked entirely.
Here’s a quick breakdown of these protocols:
v=spf1 include:spf.protection.outlook.com -all.v=DMARC1; p=none; to monitor your email authentication before moving to stricter enforcement.Failing to configure these protocols exposes your domain to phishing, spoofing, and other security issues. Additionally, many organizations overlook the importance of customizing anti-phishing and anti-spam policies, leaving default settings in place. This oversight can also negatively impact deliverability.
Domain verification is another critical step in maintaining a good sender reputation. Using unverified domains or third-party platforms with questionable reputations can immediately trigger Microsoft 365's spam filters.
One common issue arises when domains are partially verified. For example, incomplete DNS updates can cause emails to be flagged as coming from an "Unverified Sender", despite some setup steps being completed.
To ensure your domain is fully trusted, complete the verification process in the Microsoft 365 admin center. If there are errors, double-check your DNS records to confirm they’ve been correctly configured and fully propagated across the internet.
If you’re using a third-party platform to send emails through your Microsoft 365 domain, make sure it supports and properly implements SPF, DKIM, and DMARC. Some external services fail to do this, leading to verification problems. Tools like online DNS checkers or the nslookup command can help you troubleshoot and confirm that your records are visible to external servers.
Your sending IP address plays a huge role in determining whether your emails are treated as legitimate or flagged as spam. A poor IP reputation - especially if it’s blacklisted - can result in emails being rejected outright or dumped into spam folders.
For organizations using shared IP addresses, the actions of other senders can hurt your reputation. On the other hand, dedicated IP addresses give you more control, isolating your reputation from others. This is especially important for high-volume senders or businesses with strict deliverability needs.
To keep your IP reputation intact:
For those managing multiple domains or mailboxes, platforms like Primeforge can simplify DNS setup and provide US-based IP addresses with strong reputations. This reduces the technical burden of maintaining proper email authentication across numerous sending addresses.
Now that you're familiar with the common pitfalls, let's dive into strategies to help keep your emails out of the dreaded spam folder. The trick lies in tackling both content and technical factors while keeping your email list clean and engaged.
Your email's content is your first defense against spam filters. Stick to clear and straightforward language, and steer clear of spammy keywords like "free", "guaranteed", or "urgent." These words can set off Microsoft 365's filtering system.
Formatting also plays a big role. Avoid using all caps in subject lines, excessive exclamation marks, or mixing fonts. Instead, stick to standard fonts and keep capitalization and punctuation reasonable.
Pay attention to the balance between text and images. Emails that lean too heavily on images without enough text often get flagged. Make sure your message still makes sense even if the images don’t load.
Lastly, always include a clear reply-to address and double-check your links. Broken links or suspicious URLs are major red flags. Use domains you control and avoid generic link shorteners.
These tips work hand-in-hand with good list management and technical practices to ensure your emails land where they should: the inbox.
A clean and engaged email list is just as important as solid content. Regularly remove inactive or unengaged recipients, and segment your audience to send more personalized messages. This reduces spam complaints and boosts deliverability.
Resist the temptation to use purchased email lists or add contacts without proper consent. Sending emails to outdated or unverified addresses can hurt your sender reputation and trigger Microsoft 365's spam filters. The short-term convenience isn’t worth the long-term damage.
Beyond content, your technical setup is critical for staying out of the spam folder. Make sure your SPF, DKIM, and DMARC records are up to date.
Keep an eye on your sender reputation and check if your sending IP addresses are listed on any blocklists. Microsoft 365 uses these signals to gauge spam risk, so maintaining a good reputation is a must.
If you're using a new domain, avoid sending large volumes of emails right away. Gradually increase your sending volume to build trust with email providers.
For those juggling multiple domains or high-volume campaigns, platforms like Primeforge can simplify the process by automating key aspects of email infrastructure.
Primeforge handles automated DNS setup, US-based IP addresses, and bulk DNS management, making technical tasks easier. These tools help maintain a strong sender reputation and improve deliverability, especially for cold outreach campaigns.
The platform also automates SPF, DKIM, and DMARC management across multiple mailboxes, taking the pressure off your team while ensuring compliance with Microsoft 365's filtering requirements. With pricing between $3.50-$4.50 per mailbox per month, it supports both Google Workspace and Microsoft 365 users, offering reliable infrastructure for email delivery.
For organizations managing multiple domains or large-scale campaigns, automated DNS management and reputation monitoring can mean the difference between landing in the inbox or the spam folder.
Selecting the right email infrastructure platform is crucial to ensuring your emails meet Microsoft 365's strict deliverability standards. Building on the technical setup requirements we’ve already covered, let’s dive into how different platforms tackle deliverability challenges.
Primeforge takes a unique approach by aligning with trusted email service providers like Google Workspace and Microsoft 365. It offers dedicated US-based IP addresses, which can significantly boost deliverability by matching the infrastructure of established ESPs.
Mailforge, on the other hand, uses a shared infrastructure built around a shared IP pool. While this setup is budget-friendly and suitable for beginners, it comes with a tradeoff: your sending reputation is tied to that of other users. This can be useful in scenarios where spam complaints are anticipated, but it limits customization and control.
Infraforge provides a more advanced solution with private email infrastructure. It offers multi-IP provisioning and API control, giving you complete authority over your sending reputation. This makes it ideal for large-scale operations, though it requires a higher upfront investment and technical know-how.
All three platforms support essential DNS configurations, which, as noted earlier, play a critical role in maintaining deliverability. However, the way each platform handles IP management and customization can either strengthen or weaken these efforts.
| Platform | Infrastructure Type | IP Setup | Best For | Pricing |
|---|---|---|---|---|
| Primeforge | Google Workspace/MS365 | US-based dedicated | ESP matching, better deliverability | $3.50–$4.50 per mailbox/month |
| Mailforge | Shared email infrastructure | Shared IP pool | Beginners, cost-conscious users | Budget-friendly |
| Infraforge | Private email infrastructure | Multi-IP provisioning | Advanced users, large-scale campaigns | Higher initial investment |
When it comes to customization and control, the platforms differ significantly. Mailforge’s shared infrastructure means your email reputation is influenced by other users on the same IP pool. In contrast, Infraforge’s private setup gives you dedicated IPs, allowing you to fully manage your reputation and tailor the infrastructure to your needs.
Mailtrap takes things a step further by offering a complete email testing and delivery solution, going beyond the basic infrastructure provided by the other platforms.
When deciding between these platforms, think about your technical expertise, budget, and the scale of your email campaigns. Primeforge's ESP-matching approach is particularly effective for Microsoft 365 recipients, Mailforge offers an affordable entry point, and Infraforge provides unmatched control for enterprise-level campaigns. This comparison should help you choose the platform that aligns best with your deliverability goals and Microsoft 365's strict spam filters.
Getting your emails past Microsoft 365's spam filters takes a well-rounded strategy that balances both content and technical factors. With Microsoft 365 blocking nearly 20% of emails before they hit the inbox, preparation is everything.
This section highlights the key steps to align your email campaigns with best practices for content, technical setup, and list management.
Content matters. The way your email is written plays a huge role in deliverability. Steer clear of trigger words like "free", "urgent", or "deal" in your subject lines and body text. Keep formatting clean and professional - avoid all caps, excessive punctuation, and flashy colors. Also, strike a balance between text and images to avoid looking overly promotional.
Technical setup is crucial. Ensuring your SPF, DKIM, and DMARC records are properly configured is non-negotiable. A strong domain reputation, supported by verified sending domains and trustworthy IP addresses, significantly boosts your chances of landing in the inbox.
Manage your list wisely. Poor list management can quickly damage your sender reputation. High bounce rates and spam complaints are red flags for spam filters. Regularly clean your email list and monitor engagement to maintain strong quality signals.
Infrastructure matters too. The platform you use can either help or hurt your deliverability. For example, Primeforge provides dedicated US-based IPs, automated DNS setup, and bulk updates - features that reduce the risk of technical issues that could land your emails in spam.
For consistent success, focus on maintaining a strong sender reputation and staying proactive. Gradually increase email volume for new campaigns, monitor your deliverability metrics, and test your emails before sending them to large lists. By combining a solid technical foundation with smart content strategies, you'll improve your chances of reaching your audience's inbox in Microsoft 365 environments.
To keep your emails from being flagged as spam in Microsoft 365, start by focusing on email authentication. Implement SPF, DKIM, and DMARC records to confirm your sender identity and improve your chances of landing in the inbox. Equally important is maintaining a strong sender reputation - use professional, clear language and steer clear of spammy phrases like "limited-time offer" or overusing capital letters.
You can also take advantage of Microsoft Exchange mail flow rules to let trusted emails skip spam filters. Regularly review how your organization handles outbound emails and tweak anti-spam settings in the Microsoft Defender portal to cut down on false positives. Staying vigilant is key to ensuring your emails reliably reach their intended recipients.
For businesses relying on cold outreach, tools like Primeforge offer specialized email infrastructure solutions. These include automated DNS setup and US-based IP addresses, which can help improve deliverability and lower the chances of being marked as spam.
To improve email deliverability in Microsoft 365, start by implementing SPF, DKIM, and DMARC authentication protocols. These measures help safeguard your emails against spoofing and phishing attempts while building credibility with email servers. Gradually warm up your domain and IP address to establish a strong reputation, and keep your contact list clean by removing inactive or invalid email addresses.
Steer clear of misleading subject lines, deceptive headers, or overusing spam-triggering keywords. Regularly test your email deliverability with Microsoft’s built-in tools, and keep an eye on bounce rates to catch potential problems early. For cold outreach campaigns, you might explore tools like Primeforge, which provides customized email infrastructure, automated DNS setup, and US-based IPs to enhance deliverability.
Primeforge takes the hassle out of email deliverability by providing automated, expertly crafted email infrastructure tailored for cold outreach campaigns. With dedicated mailboxes from Google Workspace and Microsoft 365, along with proper DNS configuration and US-based IP addresses, it minimizes the risk of your emails landing in spam folders.
What sets Primeforge apart is its ability to simplify the setup process. Features like bulk DNS updates and tools for managing sender reputation make running email campaigns a breeze. These tools are designed to improve inbox placement, which can lead to better engagement and higher response rates. With Primeforge handling the technical side of deliverability, you can concentrate on building meaningful connections with your audience.