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Summary

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.

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.

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.

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.

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.

06 May 2025 - TECHCOMMUNITY.MICROSOFT.COM

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