Why is Microsoft rate limiting email sends for some customers?
Summary
What email marketers say7Marketer opinions
Email marketer from EmailDrips Blog explains that poor list hygiene practices contribute to deliverability issues. Sending emails to outdated or invalid addresses will contribute to rate limiting.
Email marketer from Stack Overflow notes that sudden spikes in email volume can trigger rate limiting, especially if the sending infrastructure isn't prepared for the increase. Gradual scaling is recommended.
Email marketer from Email Marketing Forum suggests that using shared IPs can increase the likelihood of rate limiting if other users on the same IP have poor sending reputations. A dedicated IP may offer more control.
Email marketer from SenderVerify Blog shares that a new IP address needs to be warmed up to build a positive sending reputation. Suddenly sending large volumes of email from a new IP can trigger rate limiting.
Email marketer from Random Email Blog answers that Microsoft uses feedback loops to identify senders who generate a high volume of spam complaints. If you have excessive complaints from users your emails will be rate limited.
Email marketer from Reddit explains that failing to properly authenticate your email with SPF, DKIM, and DMARC can make your emails appear suspicious to Microsoft, potentially leading to rate limiting.
Email marketer from Mailjet Blog states that the content of emails can trigger spam filters, leading to rate limiting. Using spam trigger words, excessive links, or poor HTML formatting will result in rate limits.
What the experts say4Expert opinions
Expert from Spam Resource shares that Microsoft imposes limits on the number of connections that can be made from a single IP address. Exceeding these connection limits can result in temporary throttling.
Expert from Spam Resource explains that Microsoft actively monitors complaint rates and throttles senders who exceed acceptable thresholds. Even legitimate senders can be affected if they generate too many complaints.
Expert from Word to the Wise discusses that low engagement rates (e.g., low open rates, few clicks) can signal to Microsoft that the emails are unwanted, leading to decreased deliverability and potential throttling.
Expert from Email Geeks suggests the rate limiting issue may occur if customers are sending to both O365 addresses and free Microsoft domains simultaneously, potentially exceeding the limits on all their domains. This could explain why only some customers are affected.
What the documentation says3Technical articles
Documentation from Microsoft Learn indicates that exceeding the allowed number of simultaneous connections to Exchange Online can trigger rate limiting. Managing the number of connections is crucial for maintaining optimal sending rates.
Documentation from Microsoft Learn highlights that sender reputation plays a significant role in deliverability. Poor sender reputation, based on factors like spam complaints or sending to invalid addresses, can lead to rate limiting or blocking.
Documentation from Microsoft Learn explains that Exchange Online uses throttling to manage resources and maintain reliability. Rate limiting can occur when sending patterns resemble those of malicious attacks, causing temporary blocks.