Email throttling is where an ISP limits or throttles the amount of email a sender can send in a certain period, resulting in higher bounces back. It can be resolved within 72 hours and depending on the situation, there can be benefits such as managing responses and server bandwidth. It can be prevented by scheduling emails to deploy over an extended period, separating marketing and transactional email traffic, and sending emails at earlier times. Working with an experienced email provider can help manage email throttling issues.
Excerpt from the main article:
Some internet service providers (ISPs) limit—or throttle—the amount of email accepted from a particular sender during a specific period. If you try to send an email above the acceptable threshold, the ISP will reject your email, resulting in higher bounces back. When ISPs throttle your emails, you’ll get a message that says something like, “user’s mailbox is over quota” or “user is receiving mail at too great a rate right now, please try again later.” A temporarily blocked delivery attempt that asks you to send the email later is a type of email throttling called a deferral. As a 400
What Is Email Throttling? How to Prevent It | Twilio SendGrid was originally published on SendGrid Email Deliverability Blog | SendGrid