Summary
Emails to O365 recipients are quarantined due to a combination of factors including aggressive filtering, poor sender reputation, issues with shared IPs, lack of proper email authentication (SPF, DKIM, DMARC), poor list hygiene, spammy content, and recipient-defined safe sender lists. Solutions involve improving IP reputation, implementing proper authentication, maintaining a clean and engaged email list, avoiding spam trigger words, testing emails, setting up feedback loops, and checking against blocklists like BRBL. O365's filtering is more aggressive, requiring strict adherence to email best practices.
Key findings
- Aggressive Filtering: O365's filtering is more aggressive than other providers, leading to quarantines.
- IP Reputation: Poor IP reputation (bad neighborhood, blocklisting) causes quarantine issues.
- Shared IP Impact: On shared IPs, others' sending practices affect your deliverability.
- Authentication: Lack of SPF, DKIM, and DMARC records causes O365 to quarantine emails.
- List Hygiene: Poor list hygiene (inactive users, bounces) negatively impacts deliverability.
- Content Filtering: O365 uses content filters to identify and quarantine spammy emails.
- Admin/User Policies: Administrator policies or user-defined safe sender lists impact deliverability.
Key considerations
- Monitor Reputation: Regularly monitor IP and domain reputation metrics.
- Implement Authentication: Properly configure SPF, DKIM, and DMARC records.
- Clean Your List: Regularly remove inactive subscribers and invalid email addresses.
- Optimize Content: Avoid spam trigger words and ensure proper email formatting.
- Set up Feedback Loops: Implement feedback loops to identify and remove complainers.
- Test Emails: Test emails with O365 to identify and fix potential issues.
- Check Blocklists: Check if your IP is on blocklists like Barracuda's BRBL and request delisting.
- SNDS Monitoring: Monitor SNDS for potential issues with Microsoft deliverability.
What email marketers say
10 marketer opinions
Emails to O365 recipients often get quarantined due to aggressive filtering, issues with IP reputation, lack of proper email authentication (SPF, DKIM, DMARC), poor list hygiene, and spammy content. Solutions involve setting up authentication records, maintaining a clean and engaged email list, monitoring and improving IP reputation, avoiding spam trigger words, and testing emails before sending.
Key opinions
- Aggressive Filtering: O365 has aggressive filters that can quarantine emails.
- IP Reputation: Poor IP reputation significantly impacts deliverability to O365.
- Authentication: Lack of proper SPF, DKIM, and DMARC records leads to quarantine.
- List Hygiene: Poor list hygiene (inactive subscribers, high bounce rates) hurts deliverability.
- Content Filtering: O365 uses content filters to identify and quarantine spammy emails.
- Shared IP Impact: Sending practices of others on shared IPs can affect your deliverability.
Key considerations
- IP Monitoring: Monitor your IP reputation regularly using tools like Sender Score.
- Authentication Setup: Ensure SPF, DKIM, and DMARC records are properly configured.
- List Cleaning: Regularly remove inactive subscribers and invalid email addresses.
- Content Optimization: Avoid spam trigger words and ensure proper HTML formatting in your emails.
- Feedback Loops: Set up feedback loops to monitor and address recipient complaints.
- Email Testing: Test emails with different email clients, including Outlook/O365, before sending.
Marketer view
Email marketer from Email Archive says that O365 uses content filters that scan emails for spam-like characteristics. Avoiding spam trigger words, using proper HTML formatting, and ensuring a good sender reputation can help prevent emails from being flagged as spam and quarantined.
31 May 2023 - Email Archive
Marketer view
Marketer from Email Geeks mentions Microsoft has aggressive filters, and this is usually the first sign you will start getting filtered on others.
1 Mar 2022 - Email Geeks
What the experts say
5 expert opinions
Emails to O365 recipients are quarantined due to a combination of factors including aggressive filtering, sender reputation issues, and improper email authentication. O365 may have additional spam filters for mail from IPs not associated with their own MX records. Identifying global versus individual filtering issues is crucial. Monitoring sender reputation, maintaining strict adherence to email best practices, and ensuring proper authentication (SPF, DKIM, DMARC) are essential to improve deliverability and prevent quarantines.
Key opinions
- Aggressive O365 Filtering: O365's filtering is more aggressive than other providers, leading to more emails being quarantined.
- Sender Reputation: Sudden drops in sender reputation or general negative reputation leads to emails getting quarantined.
- MX Record Filtering: O365 has spam filters for mail coming from IPs not their own MXs.
- Authentication Importance: Proper email authentication (SPF, DKIM, DMARC) is critical for deliverability.
Key considerations
- Identify Issue Type: Differentiate between global issues (affecting many recipients) and individual filtering issues.
- Reputation Monitoring: Regularly monitor sender reputation metrics to identify and address issues promptly.
- Authentication Configuration: Ensure SPF, DKIM, and DMARC are properly configured to authenticate your emails.
- Best Practices: Adhere strictly to email best practices including authentication, list hygiene, and engagement metrics.
- Filter Customization: Adjust custom filtering with BCL and SCL settings.
Expert view
Expert from Spam Resource explains that a sudden drop in sender reputation can cause emails to be quarantined by O365. Contributing factors include sending to invalid email addresses, sudden increases in email volume, or complaints from recipients. Regularly monitor sender reputation and address any issues promptly.
23 Dec 2022 - Spam Resource
Expert view
Expert from Email Geeks advises setting up a domain hosted by O365 for customers to send test messages to in order to differentiate between global and individual issues. ESPs can address global issues but not individual filters.
7 Jan 2022 - Email Geeks
What the documentation says
4 technical articles
Emails are quarantined in O365 due to administrator-defined policies, Exchange Online Protection (EOP), or Defender for Office 365 flagging them as spam, phishing attempts, malware, or rule matches. Administrators can release quarantined emails and report them as not a threat. Users can add senders to safe sender lists to prevent emails from going to junk. Being listed on the Barracuda Reputation Block List (BRBL) can also cause emails to be quarantined.
Key findings
- Quarantine Reasons: Emails are quarantined due to policies, EOP/Defender flagging them as spam, phishing, or malware.
- Admin Release: Administrators can release quarantined emails and report them as safe.
- Safe Sender Lists: Users can add senders to safe sender lists to bypass junk folder.
- BRBL Listing: Being listed on the Barracuda Reputation Block List (BRBL) causes quarantine.
Key considerations
- Review Policies: Review administrator-defined policies to understand quarantine triggers.
- Admin Intervention: Admins should regularly review quarantined emails and release legitimate ones.
- User Education: Educate users on how to add senders to safe sender lists.
- Check BRBL: Check if your IP is listed on the BRBL and take steps to delist if necessary.
Technical article
Documentation from Microsoft Learn explains that emails are quarantined due to policies set by administrators or automatically by Exchange Online Protection (EOP) or Defender for Office 365. Reasons include suspected spam, phishing attempts, malware, or rule matches.
1 Apr 2022 - Microsoft Learn
Technical article
Documentation from Barracuda explains that one reason for emails being quarantined is if the sending IP address is listed on the Barracuda Reputation Block List (BRBL). They provide tools and methods to check if your IP is listed and steps to request delisting.
27 Jun 2021 - Barracuda Networks
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