Using Microsoft O365 for business email does not inherently disadvantage your email deliverability. While some perceive that using an in-house email service like O365 might grant an unfair advantage (or disadvantage) with Microsoft's filters, industry experts and internal policies suggest that all senders, including Microsoft's own marketing teams, are subject to the same rigorous filtering standards. However, the unique behavior of Microsoft's filters, particularly when sending within the O365 network, can lead to distinct deliverability experiences compared to sending to other providers like Gmail. Adhering to email best practices, regardless of your email service provider, remains paramount for inbox placement.
Key findings
Equal treatment: Microsoft's stated policy and common expert opinion indicate that all senders, including those using O365 business domains, are treated equally by their filters to avoid anti-trust concerns. This means no inherent deliverability boost or penalty simply for using their service.
Internal filtering: Even Microsoft's own emails can sometimes land in the O365 spam folder, underscoring the strict and universal application of their spam filters. This highlights the importance of universal email deliverability best practices regardless of who you are sending to. If you are struggling with this, refer to our guide on how to improve email deliverability with Microsoft.
Different filter sets: While there's no intentional favoritism, emails sent from O365 to O365 recipients are processed by Microsoft's specific filters, which can behave differently than, say, Gmail's filters when sending to Gmail recipients. These Microsoft filters are sometimes perceived as 'wacky' or unpredictable by senders. Discover more about why Microsoft email deliverability issues are unusually bad.
Source knowledge: O365's internal knowledge of a sender's authenticity and mail volume when sending within its network could potentially have an unintended effect on deliverability, even if not part of an intentional policy to favor O365 users.
Key considerations
Authentication standards: Regardless of O365 usage, adhering to robust email authentication standards like SPF, DKIM, and DMARC is crucial. Microsoft, like other major mailbox providers, increasingly requires these for optimal deliverability. See Microsoft's email deliverability guidelines for more information.
Sender reputation: Your sender reputation, built on factors like bounce rates, spam complaints, and engagement, significantly impacts deliverability to Microsoft and other ISPs. O365 usage alone won't compensate for a poor reputation.
Content and user engagement: Even with perfect technical setup, content quality and positive user engagement (opens, clicks, replies) are vital. Irrelevant or unwanted emails, regardless of origin, are more likely to be filtered to spam.
Monitoring and troubleshooting: Proactive monitoring of your email performance and quick troubleshooting of any deliverability issues within O365 are essential to maintain good inbox placement.
What email marketers say
Among email marketers, there's a mix of experiences and theories regarding O365's impact on deliverability. While some share frustrations about Microsoft's strict filtering, even for its own messages, others ponder whether there might be subtle, perhaps unintentional, advantages when sending within the O365 ecosystem. The consensus leans towards the idea that fundamental best practices override any perceived provider-specific quirks, but the 'wacky' nature of Microsoft's filters is a common talking point.
Key opinions
Universal frustration: Many marketers express humor and frustration at Microsoft's stringent filtering, noting that even Microsoft's own communications sometimes land in the spam folder within O365 environments.
No measurable difference: Some marketers believe that using O365 business domains does not result in any noticeable difference in deliverability to Microsoft endpoints, suggesting a level playing field.
Internal perception: There's anecdotal discussion about whether sending from O365 to O365 offers an unintentional leg up due to O365's internal knowledge of the sender's authenticity and volume.
Separate filtering: Marketers recognize that sending from O365 to Gmail involves Gmail's filters, while O365 to O365 involves Microsoft's filters, which are often described as unpredictable. Your choice of email tool affects deliverability.
Key considerations
Adherence to best practices: Marketers understand that regardless of the email service, foundational best practices like maintaining a clean list, engaging content, and proper authentication are critical for deliverability.
Domain reputation over platform: The focus should be on building and maintaining a strong sender and domain reputation rather than relying on the email service provider itself for deliverability advantages. This includes careful consideration of factors like sending a single email to multiple people.
Adapting to provider quirks: Successful marketers learn to navigate the specific filtering behaviors of different ISPs, including Microsoft, to optimize their inbox placement. For a deeper dive, read about Outlook vs Office 365 deliverability.
Data-driven strategies: While some strategies like sending within the network exist, marketers question if these are based on solid data or merely anecdotal wisdom.
Marketer view
An email marketer from Email Geeks wondered if business or custom domains utilizing O365 have any effect on deliverability concerning SNDS or Microsoft's overall systems. They were curious about any potential impact that this specific setup might have on their email reaching the inbox.
19 Dec 2023 - Email Geeks
Marketer view
A marketer from SendLayer advises that if you're struggling with Outlook deliverability, focusing on strong authentication protocols such as SPF, DKIM, and DMARC is essential. They also recommend implementing smart sender practices to significantly improve inbox placement.
24 Apr 2025 - SendLayer
What the experts say
Email deliverability experts largely agree that major email providers, including Microsoft, strive for a neutral playing field, applying their filtering rules consistently across all senders to avoid anti-trust implications. However, experts also acknowledge the complexity of filtering, noting that internal O365-to-O365 email flows might behave uniquely due to Microsoft's comprehensive knowledge of its internal networks. While intentional favoritism is denied, the nuances of filter application can lead to varied experiences.
Key opinions
No measurable impact: Experts generally state that using a business or custom domain with O365 does not have a measurable impact on deliverability. There's no inherent advantage or disadvantage observed.
Anti-trust considerations: Major email providers, including Microsoft, are careful not to favor their own emails over others due to potential anti-trust concerns, ensuring a level playing field for all senders.
Equal treatment for all: From an expert perspective, all senders, even internal marketing teams, are subject to the same best practices and filtering rules. Deliverability depends on compliance, not affiliation.
Unintentional side effects: While not intentional, experts ponder if unintended filtering side effects or O365's internal knowledge of a sender might provide a subtle leg up for O365-to-O365 communication. To learn more about common failures, read our expert guide to email deliverability.
Key considerations
Adherence to best practices: Experts consistently emphasize that adherence to email best practices, regardless of the platform, is the most crucial factor for successful inbox placement. This includes maintaining a healthy list and sending relevant content.
Understanding filter behavior: Senders need to understand that different receiving environments (e.g., O365 vs. Gmail) apply their own unique filtering rules. While Microsoft's filters can be seen as wacky at times, adapting to them is key.
Technical compliance: Proper implementation of authentication mechanisms like SPF, DKIM, and DMARC is non-negotiable for improving deliverability, particularly with Microsoft. See our blog on technical solutions from top performing senders.
Proactive engagement: To stay ahead, senders should regularly review guidelines like Outlook's new requirements for high-volume senders to ensure their practices align with the latest ISP expectations.
Expert view
An expert from Email Geeks states that using business or custom domains with O365 does not measurably affect email deliverability. This suggests that the platform choice itself does not confer any significant advantage or disadvantage in terms of reaching the inbox.
19 Dec 2023 - Email Geeks
Expert view
An expert from SpamResource underlines the critical role that domain reputation plays in achieving successful email deliverability. They emphasize that maintaining a positive reputation is fundamental for ensuring emails consistently reach their intended recipients.
15 Mar 2024 - SpamResource
What the documentation says
Official documentation and industry reports highlight Microsoft's commitment to a secure email ecosystem, often implying strict, universally applied rules rather than preferential treatment for O365 users. Recent changes, particularly from May 2025, indicate a tightening of deliverability requirements for bulk senders, emphasizing strong authentication like DMARC. These guidelines focus on sender compliance and best practices to combat spam and phishing, reinforcing that deliverability is earned through technical diligence and good sending habits.
Key findings
Stricter bulk sending rules: Microsoft is implementing stricter deliverability rules for bulk emailers starting May 2025, aiming to enhance the overall security of the email ecosystem.
DMARC requirement: For B2B brands, DMARC implementation is increasingly critical to reach a significant portion of their audience, with its absence potentially leading to emails being marked as suspicious. Learn more in our guide on a simple guide to DMARC, SPF, and DKIM.
SPF temperror: Documentation points out that SPF temperror can cause temporary delivery issues, often due to DNS timeouts.
Troubleshooting tools: Microsoft 365 Business Standard includes tools like Exchange Admin Center and Message Trace for troubleshooting email delivery problems.
Key considerations
Compliance with updated requirements: Businesses using O365 for sending must stay informed and compliant with Microsoft's evolving email sending requirements to ensure continued deliverability. Our guide on how to comply with Outlook's new sender requirements can help.
Importance of DMARC: DMARC compliance is highlighted as essential, as its absence can lead to emails being flagged and deliverability being harmed.
Email authentication is key: The changes emphasize the broader ecosystem's security, reinforcing the need for proper authentication beyond just SPF and DKIM. For instance, read more about Microsoft email authentication changes in 2025.
Proactive monitoring: Leveraging built-in Microsoft 365 tools and understanding report metrics are crucial for identifying and resolving deliverability issues.
Technical article
Documentation from MarketingProfs highlights that B2B brands are now required to have DMARC implemented to reach an average of 96% of their email marketing audience. This statistic underscores the increasing importance of DMARC compliance for successful email delivery in the business sector.
20 May 2025 - MarketingProfs
Technical article
Documentation from TechCommunity.Microsoft.com describes how an SPF temperror is not a permanent failure but can still significantly impact email delivery. It clarifies that such errors frequently occur due to issues like DNS timeouts, requiring attention to network configurations.