Summary
Email sending speed is not a fixed metric, but rather a dynamic process dictated by how quickly recipient Internet Service Providers, or ISPs, accept mail. Acceptable speeds are highly variable, depending on your sender reputation, list quality, and the specific recipient domains. Email Service Providers (ESPs) and ISPs frequently throttle or pause email delivery. This is a critical protective measure, implemented to comply with ISP-specific rate limits, manage the immense volume of incoming mail, prevent network congestion, and ultimately safeguard sender reputations-both for individual senders and the shared IP pools used by ESPs. Such slowdowns are often a result of 'back-off logic' triggered by temporary failures, high bounce rates, or reputation-related issues, all designed to ensure emails are delivered effectively and not flagged as spam.
Key findings
- Dynamic Speed: Acceptable email sending speed is not a fixed number but dynamically adjusts based on the recipient ISP's capacity, the sender's reputation, and the overall quality of the email list.
- ISP Acceptance: The true measure of sending speed is how quickly recipient ISPs accept your mail, not just how fast your ESP can send it; sending too quickly can lead to deferrals or blocks.
- Reputation Driven: Sender reputation, particularly at the domain level, and audience engagement are the primary drivers of ISP tolerance for email volume and frequency.
- Back-off Logic: Unexpected pauses or slowdowns often stem from 'back-off logic' implemented by mail servers in response to SMTP errors, temporary recipient domain failures, or reputation-triggered throttling processes.
- Throttling as Protection: ESPs and ISPs actively throttle or pause delivery to maintain positive sender reputations for shared IPs, comply with ISP sending limits, prevent spam and blacklisting, and manage server load.
- IP Warm-up: For new IPs or domains, gradually increasing sending volume-known as IP warm-up-is crucial to establish trust and achieve higher sending speeds without issues.
Key considerations
- Trust Your ESP: Rely on your Email Service Provider's deliverability team for guidance on sending rates, as they possess current, specialized experience and may adopt a conservative, but effective, approach.
- Inquire About Limits: If you experience slowdowns, ask your email vendor for a clear explanation, specifically inquiring if the issues are widespread or pertain to particular ISPs or Mailbox Providers, then work to improve reputation.
- Throttling is Normal: Understand that email throttling is a common and fundamental practice by Mailbox Providers, designed to manage incoming mail streams, prevent abuse, and protect their systems, and is not always an indictment of sender quality.
- Improve Reputation: Focus on consistently sending high-quality, wanted mail, proactively running 'add to address book' campaigns, and maintaining a clean list to bolster sender reputation, which significantly influences ISP tolerance.
- Strategic Sending: For urgent, high-volume sends, consider strategies such as splitting traffic to different ESP accounts or utilizing a dedicated IP to better manage ISP expectations and deliverability.
- SenderScore Limitations: Be aware that SenderScore is not always a reliable or complete indicator for diagnosing all complex sending issues.
What email marketers say
12 marketer opinions
The concept of an 'acceptable' email sending speed is not fixed but rather fluid, adapting primarily to the capacity and willingness of receiving Internet Service Providers (ISPs) to accept mail. This speed is significantly influenced by the sender's reputation, the quality of their mailing list, and the specific recipient domain's policies. Email Service Providers (ESPs) and ISPs routinely employ throttling or temporary pauses in delivery as a foundational protective measure. These actions are vital for managing the enormous volume of incoming email, preventing network congestion, and, most importantly, for safeguarding both individual sender reputations and the collective reputation of the ESP's shared IP addresses. Such deliberate slowdowns, often stemming from 'back-off logic,' are triggered by various factors like temporary rejections, high bounce rates, or excessive spam complaints, all with the overarching goal of ensuring effective inbox placement and preventing permanent blocks or blacklisting.
Key opinions
- Dynamic Speed: There is no single 'acceptable' email sending speed; it is highly dynamic and depends primarily on how quickly recipient Internet Service Providers (ISPs) accept mail, rather than simply how fast an ESP can send it.
- Reputation Dictates Acceptance: The true speed at which emails are delivered is governed by your sender and domain reputation, audience engagement, and list quality, with higher reputation leading to greater ISP tolerance for volume and frequency.
- ESPs Throttle for Protection: Email Service Providers (ESPs) and ISPs intentionally throttle or pause delivery to protect shared IP reputations, prevent blacklisting from high bounce rates or spam complaints, manage server load, and comply with ISP-specific rate limits.
- Back-off Logic: Unexpected slowdowns or pauses are often due to 'back-off logic' implemented by mail servers in response to temporary SMTP errors from receiving servers, or unoptimized throttling logic that attempts to safeguard deliverability.
- Warm-up is Essential: For new domains or IP addresses, a gradual increase in sending volume-known as IP and domain warm-up-is critical to establish trust and avoid triggering spam filters or blocks.
Key considerations
- Consult Your ESP: For specific advice on sending rates and to understand any current slowdowns, always consult your Email Service Provider's deliverability team, as they have up-to-date insights and can explain issues pertaining to specific ISPs or general network conditions.
- Prioritize Reputation: Actively build and maintain a strong sender reputation through consistent sending of wanted mail, maintaining clean lists, and encouraging 'add to address book' actions; this significantly impacts ISP tolerance for your email volume.
- Understand Throttling: Recognize that throttling and pausing by ESPs and ISPs are standard, proactive measures designed to manage mail flow, prevent abuse, and protect overall system stability and deliverability, not necessarily a sign of poor performance.
- Strategic Volume Management: For urgent or exceptionally high-volume sends, consider advanced strategies like splitting email traffic across different ESP accounts or utilizing a dedicated IP to better manage ISP expectations and improve deliverability.
Marketer view
Marketer from Email Geeks explains that email sending speed isn't just about how fast an ESP *sends* mail, but how fast recipient ISPs *accept* it. Sending too quickly can lead to deferrals or blocks. He advises trusting the ESP's deliverability team on sending rates, as they have current experience, even if their approach is conservative. He also notes that 480 emails/minute seems slow, but emphasizes that raw sending speed doesn't guarantee delivery if mail is deferred or queued by ISPs.
15 Jul 2021 - Email Geeks
Marketer view
Marketer from Email Geeks suggests that unexpected email sending pauses or slowdowns could be due to "backoff logic" implemented by mail servers in response to SMTP errors from receiving servers, or unoptimized throttling logic that stops sending after a certain message threshold. He notes that various configuration possibilities and infrastructure designs, business policies, and ISP delivery requirements can lead to less-than-optimal sending behavior.
18 Jun 2022 - Email Geeks
What the experts say
4 expert opinions
Acceptable email sending speeds are fluid, determined by how quickly recipient Internet Service Providers (ISPs) can process incoming mail and by your sender reputation. Email Service Providers (ESPs) and ISPs commonly implement throttling or temporary pauses in delivery. These actions are standard practice, serving as vital protective measures to manage the vast stream of emails, prevent system overload, and guard against abuse. This proactive management also allows ISPs to monitor and evaluate sender behavior and reputation, particularly for new senders or those with fluctuating volumes. Such slowdowns are often linked to 'back-off' mechanisms, which are triggered by temporary recipient domain issues, elevated bounce rates, or other reputation-related feedback.
Key opinions
- Throttling is ISP Standard Practice: Email throttling is a common and fundamental practice employed by Mailbox Providers, or ISPs, to manage incoming mail streams, prevent abuse, and protect their systems from being overwhelmed.
- Reputation-Based Throttling: ISPs use throttling to evaluate a sender's reputation, especially for new senders or those with fluctuating volumes, temporarily pausing or slowing delivery to observe behavior and mail quality.
- Back-off Mechanism Triggers: Significant slowdowns, or 'back-off' processes, are often initiated by Mail Transfer Agents (MTAs) queuing emails due to ISP-indicated throttling, temporary recipient domain failures, or reputation-triggered bounce feedback.
- SenderScore Not Always Indicative: SenderScore should not be considered a consistently reliable indicator for diagnosing many complex email sending issues.
- Not Always a Sender Problem: Throttling is not necessarily a sign of a problem with the sender but is often a normal part of how email is delivered, reflecting ISPs' efforts to manage resources and ensure mail flow.
Key considerations
- Accept Throttling as Normal: Senders should accept throttling as an inherent and fundamental aspect of email delivery, understanding that it's a primary method for ISPs to manage their networks and ensure stability.
- Prioritize Quality and Consistency: To effectively navigate throttling, focus on sending high-quality, wanted mail consistently, as this builds trust and positively influences ISP tolerance for your sending volume and speed.
- Interpret Slowdowns as Feedback: View significant email sending slowdowns, especially on dedicated IPs, as feedback related to recipient domains temporarily failing or reputation issues, prompting a need to evaluate sender practices.
- Focus on ISP Signals: Rather than solely relying on third-party scores, pay close attention to direct ISP-indicated throttling and bounce feedback, as these are direct signals about your reputation and deliverability performance.
Expert view
Expert from Email Geeks explains that Pardot might implement email rate limits based on the sender's perceived reputation or internal queue management. He suggests that pauses could also be due to Mail Transfer Agents (MTAs) queuing emails as part of a bounce or reputation-triggered back-off process, emphasizing that such significant slowdowns usually occur due to ISP-indicated throttling or bounce feedback.
10 Jul 2023 - Email Geeks
Expert view
Expert from Email Geeks clarifies that SenderScore is not always a reliable indicator for many sending issues. She suggests that the described email sending slowdown, especially on a dedicated IP, points to a "back-off" mechanism triggered by recipient domains temporarily failing, which is frequently related to sender reputation.
28 Jul 2021 - Email Geeks
What the documentation says
7 technical articles
Building on the understanding that email sending speed is inherently variable and governed by ISP acceptance, leading ESPs universally manage delivery rates. They clarify that acceptable sending speeds are not static, but rather adapt dynamically based on factors like sender reputation, the specific recipient domain's capacity, and real-time feedback from receiving servers. Email Service Providers such as Mailchimp, SendGrid, Gmail, ActiveCampaign, MailerLite, SparkPost, and Constant Contact consistently implement throttling or deferral mechanisms. These measures are critical for several reasons: to safeguard their shared IP addresses and customer reputations, adhere to strict ISP-specific sending limits, manage server load, and prevent emails from being flagged as spam or outright blocked. This proactive approach ensures optimal deliverability and maintains a healthy sending ecosystem for all users.
Key findings
- Dynamic and Reputational: Acceptable email sending speeds are not fixed; they dynamically adjust based on sender reputation, recipient domain health, and real-time feedback from receiving servers, as highlighted by Mailchimp, ActiveCampaign, MailerLite, and SparkPost.
- ESPs Prioritize Reputation: Leading ESPs like Mailchimp, SendGrid, Gmail, MailerLite, and Constant Contact throttle or pause delivery primarily to protect sender reputation-both for individual accounts and shared IP pools-and prevent blacklisting.
- Compliance with ISP Limits: Throttling is essential for ESPs to comply with varying ISP-specific sending rate limits and volume restrictions, avoiding rejections and maintaining consistent inbox placement, a point stressed by SendGrid, MailerLite, and SparkPost.
- Spam Prevention and Deliverability: A key reason for throttling is to prevent emails from being marked as spam, manage high complaint rates, or exhibit suspicious patterns, thereby ensuring overall deliverability and service integrity for users, as noted by Gmail and Constant Contact.
- IP Warm-up is Foundational: For new sending IPs or domains, a gradual increase in sending volume, known as IP warm-up, is crucial for establishing trust with ISPs and achieving higher, more stable sending speeds, according to SendGrid.
- Adaptive Delivery Algorithms: ESPs like SparkPost utilize sophisticated algorithms that adapt email delivery speed in real-time based on ISP feedback, ensuring messages are sent at a pace most likely to reach the inbox.
Key considerations
- Reliance on ESP Systems: Senders should rely on their Email Service Provider's internal systems, which are optimized to align sending speeds with recipient server capacities and best practices, as indicated by Constant Contact and ActiveCampaign.
- Throttling as a Protective Measure: Understand that ESP throttling or pausing email delivery is a standard, protective measure designed to safeguard sender reputations, ensure compliance with ISP rules, prevent rejections, and ultimately improve overall inbox placement, rather than a sign of poor performance.
- Gradual Sending for New Senders: New senders or those utilizing new IPs must gradually increase their sending volume through a diligent IP warm-up process to build trust with ISPs and avoid triggering rate limits or blocks.
- Focus on Reputation and Quality: Maintaining a strong sender reputation through consistent, high-quality, and engaged sending is the most effective way to positively influence how quickly ISPs accept your mail and minimize the need for severe throttling.
- Real-time Adaptation: Recognize that acceptable sending speeds are dynamically adjusted based on real-time feedback from recipient servers, requiring ESPs to constantly adapt delivery to ensure successful mail acceptance.
Technical article
Documentation from Mailchimp Knowledge Base explains that acceptable sending speeds are dynamic and depend on recipient domains, sender reputation, and overall email health. ESPs like Mailchimp throttle or pause email delivery to maintain a positive sender reputation for their shared IPs, comply with ISP sending limits, and prevent spam, ensuring high deliverability for all users.
4 Sep 2021 - Mailchimp Knowledge Base
Technical article
Documentation from SendGrid Docs shares that acceptable email sending speeds require gradual increases, especially for new IPs, known as IP warm-up. SendGrid throttles delivery to adhere to ISP-specific rate limits and protect sender reputation. This proactive approach prevents IP blacklisting and ensures consistent inbox placement for their customers' emails.
27 Jul 2021 - SendGrid Docs
How can staggering email sends improve sender reputation and avoid throttling?
How does email send throttling affect Gmail spam placement and overall deliverability?
What causes Comcast email throttling and how can I improve my open rates?
What is a good email sending speed and what is the minimum volume to send on a dedicated IP?
What is the best email sending speed to avoid spam folders and how does reputation affect it?
Why are emails to Microsoft domains throttled and how can deliverability be improved?
