Why is Hotmail rate limiting my transactional emails, and how can I fix it?
Summary
What email marketers say7Marketer opinions
Marketer from Email Geeks suggests that if there have been no problems for years then it is likely that a new client/clients are the problem or an existing client has changed how/what they are sending.
Email marketer from StackExchange explains using feedback loops to receive complaint data from ISPs like Hotmail, enabling you to identify and address problematic sending patterns or content that leads to negative feedback.
Email marketer from GlockApps shares that being blocked or rate limited can be due to poor list hygiene, high complaint rates, or sending spam-like content. Monitoring deliverability and using feedback loops are crucial.
Email marketer from Email Marketing Forum responds to a thread explaining that Hotmail's rate limiting could be triggered by content filters if the email text or format resembles spam, recommending A/B testing different content variations.
Email marketer from Mailjet shares that improving sender reputation involves consistent sending volumes, proper authentication (SPF, DKIM, DMARC), and managing bounce and complaint rates to avoid being rate limited by ISPs like Hotmail.
Email marketer from Reddit suggests regularly cleaning email lists to remove inactive or invalid addresses, which helps to reduce bounce rates and improve sender reputation, ultimately preventing rate limiting.
Email marketer from SendGrid explains that warming up IP addresses gradually increases sending volume to build a positive sending reputation with ISPs like Hotmail, helping to prevent rate limiting for transactional emails.
What the experts say5Expert opinions
Expert from Email Geeks explains that avenues for abuse and spam which could cause Hotmail rate limiting include outbound spam filtering, customer spamming, bounce handling, email forwarding, and forms that anyone can send mail through.
Expert from Word to the Wise explains that Hotmail has a history of deliverability problems and suggests senders should not attempt to guess at solutions but rather use reporting systems such as SNDS to understand and address the issues.
Expert from Email Geeks explains that Microsoft won't provide a specific reason for rate limiting but it is often caused by user interaction indicating unwanted mail or technical configuration issues suggesting lack of permission before sending.
Expert from Spam Resource explains using SNDS best practices by proactively addressing issues highlighted, ensuring that your IPs are not listed as problematic, and continuously monitoring your sending reputation is crucial.
Expert from Email Geeks shares that if transactional email is enough to get blocked, then the email address collection techniques of clients are likely very sloppy.
What the documentation says6Technical articles
Documentation from Microsoft Support outlines reasons for blocked emails to outlook.com and provides guidelines for resolution. It suggests reviewing sending practices, authentication setup, and content quality to address potential issues causing rate limiting.
Documentation from Microsoft SNDS explains that the Sender Network Data Services (SNDS) program allows senders to monitor the health and reputation of their sending IPs, which can help diagnose and resolve delivery issues including rate limiting.
Documentation from Microsoft Postmaster details tools and information for senders, including best practices and troubleshooting guides to help identify and resolve delivery problems to Outlook.com, such as rate limiting issues.
Documentation from DKIM details DKIM which provides a method for verifying the authenticity of email messages, ensuring that the message has not been altered during transit. Using DKIM helps establish trust with ISPs like Hotmail.
Documentation from DMARC details how it builds upon SPF and DKIM to provide a policy framework for email authentication, allowing domain owners to specify how email should be handled if it fails authentication checks, crucial to stop phishing attempts.
Documentation from RFC explains SPF records which are essential to publish a list of authorized sending sources for your domain. Proper SPF configuration helps prevent spoofing and improves deliverability, reducing the likelihood of rate limiting.