When is email throttling truly necessary for deliverability?

Email throttling can be beneficial during IP warming or when managing a list with a history of deliverability issues. It helps build trust with ISPs by sending mail at a gradual, consistent pace. However, for established senders with good reputations, extensive throttling beyond what your ESP automatically handles is often unnecessary and can delay campaign results.

Will sending emails faster cause my website to crash?

Modern web hosting, cloud infrastructure, and Content Delivery Networks (CDNs) are designed to handle significant traffic spikes. For a national brand, the clicks from an email campaign, even a large one, are unlikely to crash a well-configured website, especially if the email's Click-Through Rate (CTR) is relatively low. Website performance concerns are often rooted in outdated infrastructure or unoptimized site design.

My deliverability is high with extensive throttling, isn't that proof it works?

While extensive throttling might appear to maintain deliverability, it's more likely that your overall sender reputation is built on factors like good list hygiene, consistent sending volume over time, low complaint rates, and proper email authentication (SPF, DKIM, DMARC). These elements are far more impactful than the duration of your email send.

Should I let my Email Service Provider handle throttling or do it manually?

Many modern ESPs employ sophisticated dynamic throttling algorithms. They automatically adjust sending speeds based on real-time feedback from ISPs, optimizing for inbox placement. Letting your ESP manage this can often be more efficient and effective than manually imposing an overly cautious, lengthy throttle, as the ESP can react to changing conditions faster than a static setup.

How can I test if I can reduce my email throttling period?

Consider a gradual approach. Reduce your throttling window incrementally, for example, from 12 hours to 8, then 6, while closely monitoring your email deliverability metrics (opens, clicks, bounces, complaints) and website performance. This data-driven approach can help identify the optimal sending speed for your specific audience and infrastructure.

Is extensive email throttling beneficial for deliverability or website performance? - Technical - Email deliverability - Knowledge base

When managing large email lists, the concept of email throttling often comes up. Some marketing teams opt for extensive throttling, spreading their email sends over many hours, or even a full day. The argument is that this approach supposedly benefits email deliverability and prevents website crashes due to sudden traffic surges. However, the reality of modern email infrastructure and web performance often tells a different story. I've encountered clients with massive lists who still adhere to this lengthy throttling strategy, believing it's the key to their excellent sender reputation. Yet, other large brands manage similar or even larger volumes without such aggressive throttling, achieving comparable results.

It raises an important question: is extensive email throttling truly necessary or even beneficial in today's digital landscape? This deep dive will explore whether these long send times are still a valid strategy for maintaining high deliverability and protecting website performance, especially given advancements in email service provider (ESP) capabilities and web hosting technology. I’ll share insights on when throttling is genuinely helpful versus when it might be an outdated practice hindering efficiency.

Understanding email throttling

Email throttling is the process of intentionally slowing down the rate at which emails are sent to recipients. Internet Service Providers (ISPs), like Gmail and Microsoft, employ their own forms of throttling to manage incoming mail volume and identify potential spam, but senders can also implement it proactively. The idea is to send emails in smaller batches over time, rather than a massive burst all at once. This strategy was, and in some cases still is, recommended for several reasons.

Historically, aggressive, unthrottled sending from a new or cold IP address could quickly trigger spam filters or lead to your IP being added to a blacklist (or blocklist). ISPs look for consistent sending patterns and positive engagement. A sudden, large volume of mail from an unfamiliar sender can appear suspicious, leading to emails being rejected or sent straight to the spam folder. Throttling helped mimic the gradual email sending behavior of a legitimate sender, aiding in the warming up of IP addresses and domains.

While manual throttling can still be part of a strategic plan, especially for a new sender or a significant change in sending volume, many modern Email Service Providers (ESPs) handle much of this automatically. They have sophisticated algorithms that dynamically adjust sending rates based on ISP feedback, IP reputation, and engagement metrics, which is far more efficient than a blanket 12-hour throttle.

For a client sending 18 million emails three times a week, over four IP addresses, throttling for 10-12 hours translates to a significantly slower send rate per hour per IP than what modern infrastructure can typically handle. For instance, sending 18 million emails over two hours with four IPs would mean each IP sends approximately 2.25 million emails per hour. This is a substantial volume, but it's often within the capabilities of a well-configured ESP.

Deliverability: is longer always better?

The primary goal of email throttling, from a deliverability standpoint, is to maintain a healthy sender reputation with ISPs. A good reputation signals to ISPs that your emails are legitimate and wanted, increasing the likelihood of them landing in the inbox rather than the spam folder. Throttling can help prevent sudden spikes in volume that might overwhelm an ISP's systems or be mistaken for spam attacks.

However, claiming that extensive 10-12 hour throttling is the sole reason for high deliverability, especially when engagement metrics like click-through rates (CTR) are subpar (<1.5%), is a shaky assertion. High deliverability is usually a confluence of many factors beyond just sending speed:

List quality: A clean, engaged list with low bounce and complaint rates is paramount. Even with long throttling, a poor list will eventually tank reputation.
Content relevance: If recipients find your content valuable, they will open and click, positively impacting your reputation. Low CTR suggests content may not be resonating.
Authentication: Proper implementation of SPF, DKIM, and DMARC is critical for proving legitimacy to ISPs. These protocols build trust, regardless of sending speed.
Complaint rates: Keeping spam complaints low is essential. A slow send might slightly reduce the immediate impact of a complaint, but it doesn't solve the underlying issue of why recipients are marking your mail as spam.

It is far more likely that their strong sender reputation stems from a good overall list hygiene, consistent sending practices over time, and adherence to email authentication standards, rather than the extended throttling window itself. Many large senders successfully distribute similar volumes over much shorter periods, demonstrating that aggressive throttling for deliverability alone is often unnecessary for established senders with good practices.

Website performance considerations

The other major concern cited for extensive throttling is the fear of website crashes due to a sudden influx of traffic from email clicks. This concern might have been more valid a decade or so ago when web infrastructure was less robust. However, for a national brand or publisher, which typically has significant online presence and investment in their web infrastructure, this argument seems dated.

Consider the numbers: with an 18 million subscriber list and a sub-1.5% CTR, the total clicks generated from a single email send are relatively modest. Even if every click happened simultaneously, modern cloud hosting solutions, content delivery networks (CDNs), and scalable server architectures are designed to handle massive, instantaneous traffic spikes. Leading platforms like Amazon Web Services or Google Cloud can auto-scale resources to accommodate fluctuating demand without manual intervention.

The concern about website performance due to email-generated traffic might signal an underlying issue with the website's architecture or hosting plan. If a site cannot handle a few hundred thousand simultaneous clicks, it indicates a significant need for infrastructure upgrades or optimization. Furthermore, since the emails are not image-heavy, the immediate page load impact from the email itself is also minimized.

Optimizing send times for large volumes

Given that many major ESPs offer dynamic throttling or smart sending features, allowing your ESP to manage the send pace often yields better results. These systems are constantly analyzing ISP feedback and adjusting rates to optimize for inbox placement. Manually overriding these systems with an overly cautious, lengthy throttle might actually be leaving deliverability potential on the table by delaying engagement signals to ISPs.

One key benefit of shorter send times is the potential for more immediate engagement. When emails arrive quickly, recipients are more likely to interact with them closer to the moment of sending. This can lead to a more concentrated spike in opens and clicks, which ISPs interpret as strong positive engagement signals, further bolstering sender reputation. Spreading sends over 10-12 hours might dilute this immediate positive feedback, as recipients open and click at varied times throughout the day, or even miss the email entirely if it arrives too late.

If a client is hesitant to reduce throttling due to fear of website issues, a pragmatic approach is to conduct a controlled test. This could involve gradually decreasing the throttling window, perhaps from 12 hours to 8, then to 6, and so on, while closely monitoring both email deliverability metrics and website performance indicators. This iterative testing can provide empirical data to support a shift to shorter send times, addressing their concerns with hard evidence. It also allows for identification and resolution of any genuine website bottlenecks.

Additionally, segmenting the email list and prioritizing sends to your most engaged subscribers first can be a powerful strategy. This front-loads positive engagement signals to ISPs, building immediate trust for the rest of the send. Then, less engaged segments can follow. This is a form of intentional throttling that focuses on optimizing for positive signals rather than simply spreading out the volume.

Modern email infrastructure vs. extensive throttling

Old approach: manual, extensive throttling

Email campaigns are manually spread over 10-12 hours or more, typically to avoid perceived deliverability issues or website overloads from click spikes.

Deliverability: Relies on slow, consistent sending. May artificially inflate perception of good deliverability, but doesn't address underlying engagement or list quality issues.
Website performance: Assumes legacy web infrastructure cannot handle concentrated traffic, leading to overly cautious sending schedules.
Efficiency:Campaign insights are delayed and response windows are extended, potentially impacting real-time marketing efforts.

Modern approach: ESP-managed dynamic throttling

Leverages ESPs' advanced algorithms to dynamically adjust sending rates based on real-time feedback, ensuring optimal inbox placement.

Deliverability: Focuses on rapid positive engagement signals, sender reputation, and adherence to authentication standards (e.g., DMARC).
Website performance: Assumes modern, scalable web infrastructure capable of handling significant traffic peaks, often relying on CDNs and auto-scaling.
Efficiency: Enables faster campaign deployment, quicker performance insights, and more agile marketing responses.

It’s important to challenge outdated assumptions and assess current infrastructure. While a very fast, unthrottled send might not always be ideal, especially when warming up a new IP or domain, an excessively long throttle is often a relic of a bygone era. Modern ESPs are equipped to handle large volumes intelligently, and most established websites should be able to absorb the resulting traffic spikes without issue.

The key is finding the optimal balance between respecting ISP limits and maximizing campaign efficiency. This balance is rarely achieved through a static, prolonged throttle across an 18-million subscriber list. Instead, it relies on a combination of robust email infrastructure (usually handled by your ESP), a healthy sender reputation built on consistent good practices, and a scalable website that can confidently handle user engagement spikes.

Views from the trenches

Best practices

Leverage your ESP's dynamic throttling features, as they are designed to optimize deliverability.

Segment your list and send to your most engaged subscribers first to front-load positive signals to ISPs.

Conduct controlled tests by gradually reducing your throttling window while monitoring performance.

Invest in scalable web hosting and infrastructure to confidently handle traffic spikes from email campaigns.

Prioritize list hygiene and engagement metrics, as these are more impactful on long-term deliverability than extreme throttling.

Common pitfalls

Relying on outdated advice regarding extensive manual email throttling for large, established lists.

Assuming website will crash due to email clicks without first assessing current web infrastructure capabilities.

Overriding ESP's internal throttling mechanisms with overly cautious, manual schedules.

Failing to address the root causes of low engagement, such as poor content or list quality.

Not testing shorter send times, thus missing opportunities for faster campaign insights and efficiency.

Expert tips

Consider that extended throttling might dilute immediate engagement signals that ISPs value.

Assess whether your website's perceived fragility is a symptom of deeper infrastructure issues.

Remember that 100,000 to 200,000 clicks should not overwhelm a well-built modern website.

Use email deliverability metrics and website performance data to make informed decisions, not just historical practices.

Recognize that internal throttling might prevent effective list segmentation and re-engagement strategies.

Marketer view

Marketer from Email Geeks says the send throttle seems unnecessary, as the ESP should be managing delivery throttling for optimal speed. Modern web technologies should easily handle traffic, assuming competent IT infrastructure.

2025-07-22 - Email Geeks

Marketer view

Marketer from Email Geeks says that even with a strong connection between spreading out mail sends and website clicks, it is worth investigating how broken the website is and whether its performance has been measured against traffic.

2025-07-22 - Email Geeks

Finding the right balance

While email throttling remains a valuable tool in deliverability management, especially during IP warming or for senders with volatile reputations, an extensive 10-12 hour throttle for a well-established sender with an 18-million list and stable deliverability is likely overkill. Their current strong reputation is more attributable to overall good sending practices, list quality, and proper authentication than the duration of their send. The fear of website crashes is also often unfounded given modern web infrastructure capabilities and the actual click volumes generated by most email campaigns.

I encourage challenging these long-held assumptions through data-driven testing. Gradually reducing the throttling window and monitoring both deliverability and website performance will provide clear insights into optimal sending speeds without risking current positive outcomes. Moving towards a more efficient sending schedule can lead to quicker campaign insights and a more agile marketing approach, without compromising the hard-earned sender reputation.