Summary
Microsoft Office 365 employs a multi-layered approach to filter or block emails based on URL reputation. Exchange Online Protection (EOP) analyzes URLs using blocklists, heuristic analysis, and reputation services. Safe Links in Defender for Office 365 provides real-time scanning and rewriting, warning users or blocking access to malicious sites. Advanced Delivery allows administrators to manage allow/block lists. External blocklists like Spamhaus and Google Safe Browsing are often integrated. Factors like domain age, URL content, presence in phishing/malware databases, user reporting, and the use of URL shorteners all influence reputation. Legitimate URLs can sometimes be flagged incorrectly, and maintaining a good sender reputation, along with proactive monitoring, is crucial.
Key findings
- Multi-Layered Approach: Office 365 uses multiple methods (EOP, Safe Links, Advanced Delivery) to assess URL reputation.
- External Blocklist Integration: Integration with external blocklists (Spamhaus, Google Safe Browsing) is common.
- Reputation Factors: Factors like domain age, URL content, and phishing database presence influence reputation.
- Shortlink Impact: The use of URL shorteners can negatively affect deliverability.
- User Reporting Affects Reputation: User reporting of suspicious URLs impacts filtering decisions.
- False Positives: Legitimate URLs can sometimes be incorrectly flagged.
Key considerations
- Review EOP and Safe Links Settings: Regularly review and configure Exchange Online Protection and Safe Links settings.
- Proactive Monitoring: Proactively monitor URL reputation using tools like Google Safe Browsing.
- Minimize Shortlink Use: Minimize the use of URL shorteners to avoid potential penalties.
- Monitor Sender Reputation: Maintain a good sender reputation to minimize the impact of URL filtering.
- Test Email Deliverability: Test email deliverability with and without suspected URLs.
- Respond to Flagged URLs: Take immediate action and request a review if URLs are flagged incorrectly.
What email marketers say
10 marketer opinions
Microsoft Office 365 filters or blocks emails based on URL reputation using a combination of factors. Low-reputation URLs, often associated with phishing or malware, can lead to email quarantining or blocking. URL shorteners may negatively impact reputation, and legitimate URLs can sometimes be incorrectly flagged. User reports of suspicious URLs contribute to Microsoft's internal blocklists. Maintaining a good sender reputation is crucial, and monitoring URL reputation using tools like Google's Safe Browsing is essential for proactive management.
Key opinions
- URL Reputation Matters: Office 365 actively uses URL reputation to filter or block emails, impacting deliverability.
- Quarantine and Blocking: Emails with low-reputation URLs are often quarantined or blocked outright.
- Shorteners Impact: Using URL shorteners can negatively affect URL reputation and increase the likelihood of filtering.
- False Positives Possible: Legitimate URLs can sometimes be flagged incorrectly, leading to false positives.
- User Reporting: User reporting of suspicious URLs influences Microsoft's internal blocklists.
- Sender Reputation: Maintaining a good sender reputation is crucial as URLs significantly impact this reputation.
Key considerations
- Test Emails: Test sending emails with and without suspected URLs to gauge filtering behavior.
- Monitor Reputation: Proactively monitor URL reputation using tools like Google's Safe Browsing status checker.
- Address Flagged URLs: Take immediate action to resolve issues and request a review if URLs are flagged.
- Avoid Shorteners: Minimize the use of URL shorteners to avoid potential reputation penalties.
- Understand Shared Hosting: Be aware that shared hosting environments can sometimes lead to false positives.
Marketer view
Email marketer from Reddit explains that Office 365 uses URL reputation to determine if a message should be quarantined. If a URL is associated with phishing or malware, the email might be automatically moved to the quarantine folder.
21 May 2025 - Reddit
Marketer view
Email marketer from SenderScoreBlog explains that maintaining a good sender reputation is crucial. URLs in emails can significantly impact this reputation, and Microsoft 365 uses various reputation services to assess URLs and filter or block emails accordingly.
21 Jun 2024 - SenderScoreBlog
What the experts say
2 expert opinions
Microsoft Office 365 filters emails based on URL reputation by assessing various factors including domain age, URL content, presence in phishing/malware databases, and use of URL shorteners. Negative signals from these factors increase the likelihood of filtering or blocking. Masking URLs with shortlink services can also result in lower reputation scores and impact deliverability.
Key opinions
- Reputation Services and Signals: Microsoft employs reputation services and internal signals to assess URL safety.
- Domain Age and Content: Domain age and the content hosted on the URL are key factors in determining reputation.
- Phishing and Malware Databases: URLs present in phishing or malware databases are likely to be blocked.
- Shortlink Impact: The use of URL shorteners can negatively impact URL reputation.
Key considerations
- Avoid URL Shorteners: Minimize the use of URL shorteners to avoid being flagged as potentially malicious.
- Maintain Domain Health: Ensure your domain has a good reputation by avoiding association with spam or malicious activities.
- Monitor URL Content: Regularly review and ensure the content linked in your emails is safe and legitimate.
- Be aware of Negative Signals: Be aware that there are many negative signals that can cause your deliverability to decrease.
Expert view
Expert from Word to the Wise explains that Microsoft uses various reputation services and internal signals to determine the safety of URLs. This includes factors like the age of the domain, the content hosted on the URL, and whether the URL is present in phishing or malware databases. URLs that trigger negative signals are likely to be filtered or blocked.
27 Jun 2021 - Word to the Wise
Expert view
Expert from Spam Resource explains that Microsoft will look to see if links within an email are masked using a shortlink service like bit.ly. These are common methods used by spammers to hide a URL's destination so they are given low reputation scores which impacts deliverability.
11 Oct 2023 - Spam Resource
What the documentation says
5 technical articles
Microsoft Office 365 utilizes several mechanisms to filter or block emails based on URL reputation, primarily through Exchange Online Protection (EOP) and Safe Links in Defender for Office 365. EOP analyzes inbound message URLs for malicious content using blocklists and heuristic analysis, potentially quarantining or blocking suspicious emails. Safe Links scans and rewrites URLs in real-time, blocking malicious links and warning users about suspicious sites. Office 365 also uses Advanced Delivery to manage allow/block lists and may integrate with external blocklists like Spamhaus and Google Safe Browsing to assess URL safety.
Key findings
- EOP URL Analysis: Exchange Online Protection (EOP) analyzes URLs for malicious content using blocklists and heuristic analysis.
- Safe Links Scanning: Safe Links in Defender for Office 365 provides real-time URL scanning and rewriting to block malicious links.
- Advanced Delivery Controls: Advanced Delivery allows administrators to manage allow/block lists for IPs, domains, and URLs.
- External Blocklist Integration: Office 365 integrates with external blocklists like Spamhaus and Google Safe Browsing.
Key considerations
- Review EOP Policies: Regularly review and configure Exchange Online Protection (EOP) policies to effectively manage URL-based threats.
- Enable Safe Links: Enable and configure Safe Links in Defender for Office 365 for real-time URL protection.
- Manage Allow/Block Lists: Utilize Advanced Delivery to manage allow/block lists and bypass filtering for trusted senders.
- Stay Informed on Blocklists: Be aware of the blocklists Office 365 uses and monitor your URLs' presence on these lists.
Technical article
Documentation from Microsoft Learn explains that Exchange Online Protection (EOP) analyzes URLs in inbound messages for malicious content. If a URL is deemed suspicious, the message can be blocked or sent to quarantine depending on the configured policies. This includes checking against known blocklists and using heuristic analysis.
25 Nov 2022 - Microsoft Learn
Technical article
Documentation from Microsoft Learn details Safe Links in Defender for Office 365. It describes how Safe Links provides URL scanning and rewriting of inbound email messages. When a user clicks a link, the URL is checked in real-time before the website is accessed. Malicious links are blocked, and users are warned about suspicious sites. This helps prevent phishing and malware attacks using URL reputation.
31 Dec 2021 - Microsoft Learn
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