What is rate limiting?

Rate Limiting, or throttling

Rate limiting, or throttling, is a way for internet service providers, or ISPs, to prevent overwhelming an individual subscriber’s inbox. When you send large volumes of email to the same ISP, throttling may occur, since an ISP only allows a certain amount of connections per hour or per day. If you exceed that number, you may start to see issues with your delivery.

Rate limiting may be the culprit if you’re seeing a lot of soft bounces happening in your delivery data. Though it generally indicates that a user’s mailbox is full and you should try again later, it may also be that you’ve sent too much volume to the same ISP and are being throttled.

With rate limiting and throttling, it’s best to evaluate your overall infrastructure and make sure you have a clean email list. Are you sending to people who really want to receive your emails?

Additional Resources

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