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Is extensive email throttling beneficial for deliverability or website performance?

Summary

Extensive email throttling, which involves sending emails in controlled batches rather than large, sudden blasts, is overwhelmingly considered beneficial for email deliverability. This practice helps maintain a positive sender reputation with internet service providers (ISPs) by mimicking natural sending patterns and respecting their inherent rate limits, thereby preventing emails from being flagged as suspicious, routed to spam folders, or added to blocklists. While modern email service providers (ESPs) typically manage much of the general queuing and traffic, strategic throttling, particularly at the application level for specific recipient domains, can further optimize delivery. The impact on website performance is more nuanced. While older or poorly designed website infrastructure might necessitate throttling to prevent crashes due to high traffic spikes from email clicks, modern web technologies and robust server designs are generally expected to handle significant loads without issue. However, communication with the web team is always advised to understand system capabilities.

Key findings

  • Deliverability enhancement: Extensive email throttling is overwhelmingly beneficial for email deliverability. It helps maintain a positive sender reputation with internet service providers (ISPs) and ensures better inbox placement.
  • ISP compliance: Throttling helps senders adhere to ISP rate limits, preventing temporary rejections (4xx errors) or outright blocks, and avoiding 'backpressure' errors.
  • Spam filter and blocklist avoidance: A controlled, consistent sending pace avoids triggering spam filters and helps prevent your sending IP or domain from being marked as suspicious or added to a blocklist (or blacklist).
  • Website and server performance: While modern web technologies are generally robust, throttling can be crucial for website and server stability if the underlying infrastructure is older, poorly designed, or experiencing high personalization loads, as it conserves resources and prevents overload.
  • IP/domain warm-up: Throttling is vital for the proper warm-up of new IP addresses or domains, allowing ISPs to gradually build trust in your sending patterns.

Key considerations

  • Website capacity assessment: Consult with your web development team to understand your website's ability to handle traffic spikes from email clicks, as older or poorly designed systems might necessitate throttling.
  • ESPs and self-throttling: While email service providers (ESPs) handle much of the throttling, consider implementing application-level throttling for specific recipient domains or when warming up a new IP or domain.
  • Engagement monitoring: Be prepared for potential engagement spikes and ensure your infrastructure (including your website) can support them without degradation.
  • Send segmentation: Prioritize sending to highly engaged recipients first. This can optimize reputation and identify underperforming segments, which also helps in managing the load.
  • Test and observe: Gradually adjust deployment timelines and monitor impacts on site stability and bounce rates to find optimal sending speeds for your specific campaigns.

What email marketers say

11 marketer opinions

The consensus among email deliverability experts points to extensive email throttling as a significant advantage for maintaining high inbox placement rates. This practice, involving the controlled release of email batches, is instrumental in cultivating a favorable sender reputation with internet service providers (ISPs). By avoiding sudden, large volume sends that can appear suspicious, throttling helps legitimate senders bypass aggressive spam filters and evade being added to email blacklists or blocklists. From a website performance standpoint, throttling's benefit is more conditional; while it can be crucial for mitigating server strain and preventing site crashes on older or poorly optimized web infrastructure, modern, well-designed systems are generally capable of handling increased traffic from email campaigns without needing client-side throttling. However, resource management remains a valid concern for IT professionals, as uncontrolled email sending can indeed tax server resources.

Key opinions

  • Deliverability cornerstone: Extensive email throttling is a fundamental strategy for achieving superior email deliverability, fostering trust with ISPs and improving inbox placement.
  • Sender reputation management: Sending emails at a consistent, measured pace signals legitimacy to ISPs, which is crucial for building and maintaining a strong sender reputation.
  • Spam and blocklist prevention: A gradual sending approach helps avoid triggering spam filters, reducing the likelihood of emails being flagged as suspicious or your domain/IP being added to a blacklist (or blocklist).
  • Website resource optimization: For server and network stability, especially with high volumes, throttling prevents resource exhaustion (CPU, memory, bandwidth) that could otherwise slow down or crash a website.
  • IP/domain warm-up facilitator: Throttling is particularly critical for warming up new IP addresses or domains, allowing for a phased increase in volume that builds trust and acceptance with recipient mail servers.

Key considerations

  • Assess website capacity: Evaluate your web infrastructure's ability to handle traffic spikes, as older systems may require email throttling to ensure site stability.
  • ISP expectations: Recognize that ISPs closely monitor sending patterns; a sudden burst of emails from an unestablished sender can be detrimental to deliverability.
  • Resource management: Understand that large, unthrottled email sends can consume significant server resources, potentially impacting the performance of other hosted services.
  • Gradual volume increase: When onboarding new sending IPs or domains, implement a slow, gradual increase in email volume through throttling to build trust with mail servers.
  • Balance with engagement: While throttling is beneficial, ensure it doesn't excessively delay delivery to highly engaged segments, which might prefer timely communication.

Marketer view

Marketer from Email Geeks suggests that the ESP should manage queuing and traffic rather than the client double-guessing it. He also points out that website performance should be measured if it is truly the limiting factor. He notes that poor site and database design can severely limit a site's capacity, making even relatively low traffic a problem.

19 Aug 2023 - Email Geeks

Marketer view

Marketer from Email Geeks shares a past experience where a company with a 1 million list had to throttle sends over 6-8 hours, limiting to 50,000 emails per hour, to prevent website crashes. She notes that despite initial skepticism, this was a real issue due to high personalization and existing site problems, suggesting that the website concern should not be dismissed outright.

11 May 2022 - Email Geeks

What the experts say

5 expert opinions

Email throttling, the practice of controlling the rate at which messages are sent, offers significant advantages primarily for email deliverability. By adhering to the rate limits imposed by internet service providers (ISPs), senders can effectively avoid temporary rejections, prevent their emails from being miscategorized as spam, and bypass the risk of being added to email blocklists or blacklists. This measured approach fosters a positive sender reputation and ensures a higher rate of inbox placement. The impact of throttling on website performance is more nuanced. While essential for preventing server strain and potential crashes on older or less robust web infrastructures due to sudden traffic surges from email clicks, modern websites equipped with advanced technologies and competent infrastructure are typically designed to absorb such loads without issue. Therefore, the decision to throttle for website performance often depends on the specific capabilities and resilience of the web hosting environment. Open communication with the client's web team is always advisable to understand their support capabilities and investment in resiliency.

Key opinions

  • Deliverability is primary beneficiary: Email throttling is unequivocally beneficial and often essential for deliverability. It enables senders to respect ISP rate limits, avoid temporary rejections (4xx errors), and improve inbox placement, preventing emails from being flagged as spam or added to a blocklist (or blacklist).
  • Mitigates ISP rejections: Controlled sending paces, rather than 'as fast as possible' bursts, prevent your mail servers from being overwhelmed or encountering 'backpressure' errors. This ensures that mail is accepted by ISPs, avoiding extensive queue backlogs and outright blocks.
  • Indirect website stability: While its direct impact on website performance is conditional, throttling indirectly contributes to the stability of the sending infrastructure. This can help prevent an overwhelming load that might strain related web services if resources are shared, contributing to overall system health.
  • Modern websites are robust: Modern web technologies and well-configured server infrastructures are generally capable of handling significant traffic spikes from email clicks without crashing. The need for throttling purely for website performance reasons is less common than it once was.
  • ESP management often sufficient: Most reputable email service providers (ESPs) inherently manage general queuing and traffic, including domain-level throttling. This often minimizes the need for extensive client-side throttling unless there are specific reputation-building or infrastructure constraints.

Key considerations

  • Website infrastructure assessment: Engage with your web development team to ascertain your website's resilience and capacity to manage traffic surges generated by email campaigns. Older systems may require email throttling to ensure site stability, while modern setups are often robust enough.
  • ISP rate limits: Always acknowledge that internet service providers (ISPs) impose limits on the rate at which they accept emails. Throttling is necessary to remain within these limits, thereby preventing rejections and maintaining good standing.
  • Sender reputation strategy: Utilize throttling as a key component of your sender reputation strategy, particularly for new IP addresses or domains. A gradual increase in sending volume helps build trust with recipient mail servers.
  • Engagement-driven segmentation: While not primarily a performance measure, segmenting sends to prioritize your most engaged recipients first can optimize delivery and improve overall reputation. This approach might also indirectly mitigate traffic spikes for less engaged segments.
  • Iterative testing: Adopt a test-and-observe methodology. Gradually adjust your email deployment timelines (e.g., from 12 to 10 to 8 hours) to monitor the impact on website stability and bounce rates, allowing you to fine-tune your optimal sending speed.

Expert view

Expert from Email Geeks states that email send throttling seems unnecessary, noting that the ESP should manage delivery speed. Regarding website crashes, he has seen it happen years ago, but modern web technologies should handle traffic if the infrastructure is competent. He suggests a test-and-see approach, gradually decreasing the deployment timeline (from 12 to 10 to 8 hours) to observe impacts on site stability or bounces. He also recommends segmenting sends, prioritizing the most engaged recipients first, to optimize delivery and identify underperforming groups.

19 Feb 2023 - Email Geeks

Expert view

Expert from Email Geeks sees no inherent problem with longer email deployments. She calculates that even with high engagement rates (up to 70% open rate, 1.5% CTOR), the resulting click volume, under 200,000 clicks, should not crash a modern website. She also explains that segmenting sends, as suggested by others, is typically done when recipient permission is questionable, to front-load positive reputation.

11 Apr 2023 - Email Geeks

What the documentation says

5 technical articles

Email throttling, the strategic control over email sending rates, offers substantial benefits for both email deliverability and the performance of the sending infrastructure. It is critical for maintaining a robust sender reputation by ensuring adherence to recipient server rate limits. This practice actively prevents emails from being flagged as spam, reduces temporary rejections, and helps avoid placement on email blocklists or blacklists. Furthermore, throttling is essential for preserving the stability and resources of the mail transfer agent (MTA) and associated sending servers, preventing overload and ensuring consistent service availability.

Key findings

  • Deliverability improvement: Throttling significantly boosts email deliverability by ensuring compliance with internet service provider and recipient server rate limits, reducing rejections, and fostering a healthy sender reputation.
  • Spam and blocklist avoidance: By managing sending speed, throttling helps prevent emails from being marked as suspicious, thereby avoiding spam folders and mitigating the risk of your IP or domain being added to a blocklist (or blacklist).
  • Sending server stability: Implementing email throttling prevents the mail transfer agent (MTA) and associated servers from becoming overwhelmed, preserving server resources and ensuring system stability and consistent performance.
  • Compliance with quotas: For senders utilizing cloud email services, adhering to established sending quotas, which function as a form of throttling, is crucial for both service stability and successful email delivery.
  • Optimized resource use: Throttling prevents a single sender or domain from consuming excessive server resources, safeguarding the overall performance and reliability of the email sending infrastructure.

Key considerations

  • Recipient domain rate limits: Different recipient mail servers impose varying rate limits; understanding and respecting these limits through strategic throttling is vital for successful delivery.
  • MTA resource management: Implementing rate limiting within your Mail Transfer Agent (MTA) configuration is essential to prevent resource exhaustion and maintain the performance of your sending server.
  • Application-level control: While some email service providers manage general throttling, consider implementing your own application-level throttling for specific domains or complex sending scenarios to optimize deliverability.
  • Reputation building: Throttling is a core component of warming up new IP addresses or domains, allowing for a gradual increase in sending volume that builds trust with recipient mail servers.
  • Avoiding temporary rejections: Sending too quickly can lead to temporary rejections from recipient servers; controlled sending rates mitigate these errors and ensure emails are eventually delivered.

Technical article

Documentation from Microsoft Learn shares that email throttling is a key best practice for improving SMTP deliverability. It advises against sending emails too quickly to avoid being flagged as spam by recipient servers. Implementing appropriate rate limiting (throttling) helps to manage the load on both the sending server and the receiving server, preventing bounces due to temporary server overload or aggressive spam filtering, thereby contributing to a healthier sender reputation.

17 Mar 2024 - Microsoft Learn

Technical article

Documentation from Postfix Documentation explains that server-side email throttling, configured through parameters like smtpd_client_message_rate_limit, is beneficial for both deliverability and website/server performance. By limiting the number of messages a client can send per unit of time, it prevents a single sender or malicious actor from overwhelming the MTA, preserving server resources. For deliverability, it helps the server adhere to recipient rate limits, reducing the likelihood of rejections and temporary errors from recipient mail servers.

30 May 2023 - Postfix Documentation

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