In the field of email marketing, particularly when managing email newsletters, the term “throttling” refers to the practice of controlling the rate at which emails are sent out from a server to recipients. Throttling is implemented to ensure that emails are delivered smoothly over a set period rather than sending them all at once. This practice helps in managing server load, avoiding spam filters, and complying with email service provider limits.

What is Throttling?

Throttling involves setting a specific limit on the number of emails sent within a particular timeframe (e.g., 100 emails per minute or 1,000 emails per hour). It allows email marketers to regulate email delivery, preventing spikes that can trigger anti-spam mechanisms or overwhelm email servers. By spacing out the sending process, throttling helps maintain a good sender reputation and improve overall deliverability rates.

Implementation Examples

  1. Scheduled Campaigns: An e-commerce company might implement throttling to send promotional emails to 100,000 subscribers. Instead of sending all emails in a single batch, they could send 5,000 emails every 15 minutes over several hours.
  2. Staggered Launches: For a global newsletter with subscribers in different time zones, throttling can allow the emails to be sent gradually, ensuring that they reach recipients at optimal times based on their local time zones.
  3. Server Load Management: A small business might use throttling to balance email sending with other server activities, ensuring that their website or other services remain responsive. For example, they could limit the email send rate to 50 emails per minute to avoid server overload.
  4. ISP Guidelines Compliance: Internet Service Providers (ISPs) often have daily or hourly sending limits. Throttling can help comply with ISPs’ guidelines, such as Yahoo or Gmail’s limits, reducing the risk of emails being blocked.

Interesting Facts

  1. Improves Sender Reputation: Bursts of large email volumes can harm a sender’s reputation and lead to increased bounce rates or emails being marked as spam. Throttling helps mitigate this risk by maintaining a consistent sending pattern.
  2. Mitigates Impact of Blacklists: By controlling the pace of email delivery, throttling can help identify and isolate issues with specific email batches or recipients, reducing the risk of being blacklisted.
  3. Helps with Analytics: Staggering email sends through throttling can provide more accurate real-time engagement metrics. This allows marketers to make quick adjustments to the campaign if needed based on initial recipient responses.

Best Practices for Throttling in Email Marketing

  1. Understand ISP Limits: Familiarize yourself with the sending limits and guidelines of various ISPs to avoid triggering spam filters or delivery issues.
  2. Adjust Based on Engagement: Monitor open rates, click-through rates, and bounce rates to adjust the throttling rate. Lower the rate if you observe a significant drop in engagement or an increase in bounces.
  3. Segment Your Audience: Send emails to smaller, targeted segments rather than the entire list at once. This can reduce the burden on servers and improve personalization efforts.
  4. Test Throttle Rates: Conduct A/B tests to determine the optimal throttle rate for different types of campaigns. Understand what pace works best for your audience and content type.
  5. Use Reliable ESPs: Ensure your Email Service Provider (ESP) supports throttling and provides the necessary tools to implement it effectively. Look for ESPs that offer customizable throttling settings.
  6. Monitor Feedback Loops: Pay attention to feedback loops from ISPs and ESPs. Throttling helps manage and respond to these feedback mechanisms more effectively, improving sender reputation and email deliverability.


Throttling plays a critical role in the field of email marketing by ensuring emails are delivered efficiently and effectively without overwhelming servers, breaching ISP limits, or falling into spam traps. By implementing throttling, marketers can ensure better deliverability, maintain their sender reputation, and optimize their campaigns based on real-time analytics. Adopting best practices for throttling is essential for achieving successful email marketing campaigns and fostering long-term audience engagement. Understanding and utilizing throttling can make a significant difference in the overall impact and success of email newsletters.

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