Summary
Emails sent to Office 365 (O365) recipients being quarantined is a common and frustrating deliverability challenge for senders. This issue can stem from a variety of factors, ranging from authentication failures and poor sender reputation to specific filtering rules configured by O365 administrators. While a global O365 problem is rare, localized issues affecting certain clients or sending patterns are more frequent. Understanding the root causes, which often involve a combination of technical configurations and sender behavior, is key to diagnosing and resolving these quarantine events. Effective solutions often require a multi-pronged approach, encompassing diligent monitoring, adherence to best practices, and direct communication with affected recipients' IT teams.
Key findings
- Localized issues: Quarantine problems are often isolated to specific recipients or client sending behaviors rather than a widespread O365 outage.
- Authentication failures: Lack of proper DMARC alignment can lead O365 to assume a DMARC policy, which may result in legitimate emails being bulked or quarantined. This is a common factor in emails landing in junk folders, as explained in our guide on why emails land in Office 365 spam folders.
- IP reputation: The reputation of your sending IP addresses, whether dedicated or shared, significantly impacts deliverability. If IPs are in a bad neighborhood, they may be subject to blacklisting or blocklisting.
- Recipient-side configuration: Individual O365 domains can implement additional spam filtering or security layers that cause legitimate emails to be quarantined, especially when mail originates from external ESPs (even for internal testing).
Key considerations
- Proactive monitoring: Regularly monitor your sender reputation and email authentication records like SPF, DKIM, and DMARC to identify potential issues before they escalate.
- Engagement and permissions: Ensure your sending practices align with permission-based marketing, and encourage clients to maintain high engagement rates to build a positive sender reputation.
- Targeted testing: Set up a controlled test domain hosted by O365. This allows you to differentiate between global deliverability challenges and issues specific to individual recipient configurations, as suggested by Practical 365 regarding managing Office 365 quarantine confusion.
- Direct communication: For recipient-specific quarantines, direct engagement with the recipient's IT administration to adjust filters or add your domain to a safe sender list is often the most effective resolution.
What email marketers say
Email marketers and ESPs frequently grapple with emails being quarantined by O365. Their experiences highlight that while O365 has robust filtering, many issues are localized, requiring specific actions from either the sender or the recipient's IT team. Marketers often look for quick fixes like whitelisting, but also recognize the underlying importance of IP reputation and adherence to sending best practices.
Key opinions
- Recent uptick: Many marketers have observed a recent increase in O365 quarantines, suggesting possible changes or stricter enforcement in Microsoft's filtering algorithms.
- Recipient IT essential: Getting the recipient's IT administrator to adjust filters or add domains to safe sender lists is frequently cited as the only effective solution for specific cases.
- Internal testing issues: Even test emails sent to internal O365 domains via third-party ESPs can be quarantined, pointing to domain-level security configurations.
- IP proximity: The proximity of IP addresses within a shared pool can lead to blocklisting if neighboring senders engage in problematic behavior, affecting overall deliverability for users on those IPs.
- Aggressive filtering precursor: Microsoft's aggressive filters are often an early indicator that a sender may start experiencing filtering issues with other mailbox providers soon.
Key considerations
- Client education: It is crucial to educate clients on proper sending practices, even if enforcing them can be challenging, to maintain a healthy sender reputation and avoid issues like those outlined in why Microsoft Outlook blocks emails.
- Distinguishing issues: ESPs should set up their own O365-hosted domains for testing. This helps determine whether issues are global (affecting all O365 recipients) or isolated to specific individual recipient filters.
- DMARC alignment: Ensure DMARC alignment is correctly configured. Without it, O365 may impose a DMARC policy that causes non-aligned emails to be bulked or quarantined. This is especially relevant if you are asking why O365 marks emails from your domain as spam.
- SNDS limitations: Microsoft's Smart Network Data Services (SNDS) provides insights only for mail sent to free domains (Outlook.com, Hotmail), not for O365 business accounts, limiting its utility for these specific issues.
Marketer view
Email marketer from Email Geeks indicates that dealing with O365 quarantines is a recent and growing problem. They find that often the only effective solution is to ask the recipient's IT administrator to adjust their filters or add the sending domains to a safe senders list, which can be challenging across many clients.
Marketer view
Email marketer from Spiceworks Community shares that a specific forwarding configuration was causing their O365 quarantine issues. They resolved it by having the recipient's domain added to a trusted list to ensure emails are always accepted.
What the experts say
Experts in email deliverability stress that O365's robust filtering demands a sophisticated approach to email authentication and sender reputation. They highlight the importance of understanding the intricate details of Microsoft's filtering mechanisms, including reputation scores and DMARC policy enforcement, to prevent emails from being quarantined.
Key opinions
- Authentication is foundational: Proper configuration of SPF, DKIM, and DMARC is not just a best practice, but a prerequisite for avoiding O365 quarantine. Our guide to fixing common DMARC issues can assist.
- Monitoring reputation scores: Understanding O365's SCL (Spam Confidence Level) and BCL (Bulk Complaint Level) scores is crucial, as these directly influence filtering decisions and indicate potential issues with sender behavior or content. Learn more about high BCL scores.
- Proactive detection: Instead of reacting to recipient complaints, experts recommend using advanced tools and strategies to identify and mitigate deliverability issues early.
- Behavioral factors: Beyond technical setup, poor sending habits, low engagement, and high complaint rates can swiftly damage sender reputation, leading to quarantines by sensitive filters.
Key considerations
- DMARC policy implications: Transitioning a DMARC policy to quarantine or reject requires meticulous monitoring to prevent legitimate emails from being affected, as discussed in how to safely transition your DMARC policy.
- Third-party sending complexities: When using ESPs, ensuring proper DMARC alignment is critical because O365 may apply its own policy if alignment is missing, leading to unexpected quarantines.
- Shared IP risks: While shared IPs can be cost-effective, they come with the inherent risk of other senders' bad practices impacting your own deliverability, necessitating vigilant blocklist monitoring and quick remediation.
- Content optimization: Beyond technical configurations, the quality and relevance of email content, along with consistent positive engagement from recipients, are vital for bypassing O365's sophisticated spam filters.
Expert view
Deliverability expert from SpamResource emphasizes that consistent adherence to email sending best practices, including list hygiene and content relevance, is the most reliable way to maintain good sender reputation and avoid filtering issues with large mailbox providers like Microsoft.
Expert view
Email expert from Word to the Wise suggests that understanding how different receivers interpret DMARC policies, especially when a policy is assumed in the absence of explicit alignment, is crucial for avoiding unexpected quarantines in O365 environments.
What the documentation says
Official documentation from Microsoft and related technical resources provides crucial insights into how O365's Exchange Online Protection (EOP) operates, including its quarantine mechanisms. These sources explain the purpose of quarantine, the types of threats it targets, and how administrators can manage quarantined messages and configure policies to mitigate deliverability issues.
Key findings
- Threat defense: Emails are quarantined when Exchange Online Protection identifies them as potential threats, including spam, malware, or phishing attempts, as noted by Medha Cloud's explanation of Microsoft 365 quarantined emails.
- Administrative control: O365 administrators have tools to audit, release, and manage quarantined messages, and can configure end-user allow and block lists within Microsoft Defender.
- Policy enforcement: Quarantine actions are driven by security policies and rules, including those derived from email authentication protocols like DMARC. Even if SPF fails, an email might not be quarantined for various reasons, as described by DuoCircle regarding SPF=Fail scenarios.
- Spam Confidence Level (SCL): Messages are assigned an SCL score, and those exceeding a certain threshold are typically moved to quarantine or junk folders.
Key considerations
- Regular review: It is important for both administrators and end-users to periodically review quarantined messages to ensure legitimate emails are not inadvertently blocked.
- Header analysis: Examining email headers for SCL and BCL scores, along with authentication results, provides crucial diagnostic information regarding O365's filtering decisions.
- Safe sender configuration: Administrators can add trusted domains or senders to allow lists to bypass some filtering, though this should be done cautiously.
- Advanced Threat Protection: Microsoft 365's Advanced Threat Protection (ATP) adds layers of security that can occasionally quarantine legitimate emails if they trigger suspicious behavioral patterns.
Technical article
Documentation from Practical 365 confirms that email quarantine occurs when a message or its content is flagged as potentially harmful to the recipient, acting as a protective measure within O365.
Technical article
A blog from Spotler advises verifying email authentication, checking sending history, and reviewing email headers for SCL and BCL scores as key steps to address emails landing in junk or quarantine in Microsoft Outlook.
Related resources
6 resources
Related pages
How to troubleshoot and resolve outlook email deliverability and spam filtering issues?
Why are my emails landing in office 365 spam folders?
Why did changing DMARC policy to quarantine send emails to spam, and how to fix it?
Why is Microsoft outlook blocking my email and how can i fix it?
Why does O365 mark emails from my domain sent via a third-party ESP as spam?
How to handle Microsoft treating DMARC reject policy as quarantine?
Why are my emails marked with a high BCL score and landing in junk folders, and how can I fix it?
How to fix common DMARC issues in Microsoft 365 and Google Workspace
How to safely transition your DMARC policy to quarantine or reject
Why your emails are going to spam in 2024 and how to fix it
