Summary
Microsoft temporarily rate limits emails due to a combination of IP and URL reputation issues, heavily influenced by sender reputation, user engagement, and content quality. A poor IP reputation, URLs associated with malicious content or spam, low engagement rates, and the use of URL shorteners can trigger rate limiting. Microsoft actively uses reputation filters, including its SmartScreen filter, to evaluate both IP and domain reputations, and new domains face stricter filtering until a good reputation is established. Being listed on blocklists almost guarantees rate limiting or blocking.
Key findings
- Reputation Driven: Microsoft's rate limiting is primarily driven by IP and URL reputation.
- Engagement Matters: User engagement (or lack thereof) significantly impacts sender reputation and deliverability.
- URL Risks: Malicious URLs and URL shorteners are red flags for Microsoft's filters.
- New Domain Challenges: New domains are subject to stricter scrutiny.
- Blocklist Impact: Blocklist presence almost always results in rate limiting or blocking.
- Comprehensive Filters: Microsoft employs multiple filters, including SmartScreen, to evaluate reputation.
Key considerations
- Monitor Reputation: Actively monitor IP and domain reputation to identify and address issues promptly.
- Improve Engagement: Focus on improving email engagement to signal trustworthiness to Microsoft.
- Avoid Risky URLs: Avoid using URL shorteners and ensure all URLs are safe and reputable.
- Establish Domain Reputation: For new domains, focus on building a positive sending reputation gradually.
- Monitor Blocklists: Monitor blocklists regularly and take immediate action to be removed if listed.
- Authenticate Emails: Implement and maintain SPF, DKIM, and DMARC records for proper authentication.
What email marketers say
10 marketer opinions
Microsoft temporarily rate limits emails due to issues with IP and URL reputation, often triggered by spam-like behavior, low engagement rates, or blocklist appearances. Microsoft's filtering algorithms factor in sender reputation, content quality, user engagement, and URL reputation when deciding whether to rate limit or block emails. URL shorteners, newly registered domains, and poor authentication practices also increase the likelihood of rate limiting.
Key opinions
- Reputation Impact: Poor IP and URL reputation are primary triggers for Microsoft's rate limiting.
- Engagement Matters: Low engagement rates (lack of opens/clicks) negatively affect sender reputation, leading to throttling.
- URL Risks: URLs associated with phishing, malware, or even URL shorteners can lead to rate limiting.
- New Domains: Newly registered domains face stricter filtering until they establish a positive reputation.
- Blocklist Impact: Listing on a blocklist almost guarantees rate limiting or blocking by Microsoft.
- Authentication is key: Ensuring proper authentication (SPF, DKIM, DMARC) is crucial for maintaining a good reputation.
Key considerations
- Monitor Reputation: Actively monitor IP and domain reputation to identify and address issues promptly.
- Clean Lists: Engage in regular list cleaning to remove unengaged or inactive subscribers.
- Authenticate Emails: Implement SPF, DKIM, and DMARC to verify sender identity and improve deliverability.
- Avoid Shorteners: Use full URLs instead of URL shorteners whenever possible.
- Engagement Strategies: Focus on creating engaging content to encourage user interaction and improve engagement metrics.
- Blocklist Monitoring: Monitor blocklists to ensure you are not listed and take action to be removed if necessary.
Marketer view
Email marketer from Email Marketing Forum mentions that they had issues with Microsoft because their domain was newly registered. Microsoft's filtering can be stricter for new domains until they establish a good reputation.
30 May 2023 - Email Marketing Forum
Marketer view
Email marketer from GlockApps suggests actively monitoring blocklists, explaining that if your IP or domain ends up on a blocklist, Microsoft is highly likely to rate limit or block your emails.
25 Feb 2022 - GlockApps
What the experts say
6 expert opinions
Microsoft's temporary rate limiting of emails due to IP/URL reputation stems from various factors. Microsoft heavily weighs sender reputation metrics and actively filters incoming emails based on these. URL shorteners can trigger penalties due to their masking potential. Microsoft's SmartScreen filter evaluates IP and domain reputation, and user engagement plays a crucial role, with low interaction impacting sender reputation and leading to rate limiting. Additionally, bounces can be message-specific, suggesting content also impacts deliverability.
Key opinions
- Sender Reputation: Microsoft heavily relies on sender reputation to determine deliverability.
- URL Shorteners: Using URL shorteners can negatively impact deliverability, particularly with Microsoft.
- SmartScreen Filter: Microsoft's SmartScreen filter analyzes IP and domain reputation.
- User Engagement: Low user engagement (e.g., low open rates) contributes to rate limiting.
- Message Specificity: Bounces can be specific to the message content itself.
Key considerations
- Monitor Reputation: Continuously monitor sender reputation to identify potential issues.
- Avoid URL Shorteners: Minimize the use of URL shorteners to avoid triggering filters.
- Improve Engagement: Focus on improving user engagement with your emails.
- Content Quality: Ensure that the content is not spammy or harmful.
Expert view
Expert from Email Geeks shares their experience of seeing the same error for one client but not another on the same IP. While acknowledging it could be IP reputation, they suggest it might also be a message-specific bounce from Microsoft.
11 Sep 2021 - Email Geeks
Expert view
Expert from Word to the Wise explains that Microsoft places a high value on user engagement. If recipients rarely open or interact with emails from a particular sender, it can negatively impact sender reputation and lead to rate limiting.
15 Jan 2025 - Word to the Wise
What the documentation says
4 technical articles
Microsoft temporarily rate limits emails due to poor IP and URL reputation, utilizing these as key factors in deciding whether to accept, rate limit, or block incoming mail. Microsoft Defender for Office 365 scans URLs for malicious content, rate limiting or blocking emails with flagged URLs. Microsoft employs rate limiting as a mechanism to safeguard its infrastructure and users from spam. Reputation filters evaluate both IP and domain reputations to identify malicious senders and URLs.
Key findings
- IP Reputation: Poor IP reputation directly leads to rate limiting or blocking by Microsoft.
- URL Scanning: Microsoft Defender actively scans URLs for malicious content.
- Protection Mechanism: Rate limiting serves as a protective measure against spam and malicious activity.
- Comprehensive Evaluation: Reputation filters assess both IP and domain reputations.
Key considerations
- Maintain IP Reputation: Proactively manage IP reputation to avoid triggering rate limits.
- URL Security: Ensure that URLs within emails are safe and free of malicious content.
- Infrastructure Protection: Understand rate limiting as a standard measure to protect email infrastructure.
- Reputation Monitoring: Continuously monitor both IP and domain reputations.
Technical article
Documentation from SparkPost explains that Microsoft, like many email providers, uses rate limiting as a mechanism to protect their infrastructure and users from spam. If your sending IP or the URLs in your emails have a poor reputation, you are more likely to be rate limited.
16 Jun 2024 - SparkPost
Technical article
Documentation from Microsoft Learn explains that Microsoft uses IP reputation as one factor in determining whether to accept email from a particular source. Poor IP reputation can lead to temporary rate limiting or blocking.
29 Aug 2024 - Microsoft Learn
Are Bitly links bad for email deliverability?
Are HTTP links penalized by spam filters in email marketing?
How can I improve email deliverability with Microsoft and avoid spam filters?
How can I resolve Microsoft Outlook S3140 errors blocking my transactional emails?
How do I handle clients concerned about emails landing in Gmail promotions tab?
Why are emails from a new .uk domain going to spam folders?
