Suped

Summary

The speed at which an email service provider (ESP) can send a large volume of emails is a common question, yet the answer is far from simple. While the underlying Mail Transfer Agent (MTA) software is capable of very high throughput, the actual sending speed is heavily influenced by a myriad of factors, primarily revolving around sender reputation, recipient Mailbox Provider (MBP) policies, and the ESP's infrastructure and practices. Benchmarking email sending speeds is complex because hypothetical maximums rarely reflect real-world delivery times, which are often intentionally throttled for optimal deliverability.

What email marketers say

Email marketers often seek clear benchmarks for ESP sending speeds to manage client expectations and campaign timing. However, many find that raw speed metrics provided by ESPs during sales cycles can be deceptive. The practical experience of marketers suggests that actual delivery times are less about the ESP's theoretical maximum throughput and more about the interplay of sender reputation, mailbox provider reception policies, and the complexity of the email content itself. Variations in delivery speed between different ESPs for the same list size are commonly observed, highlighting the nuanced nature of email throughput.

Marketer view

Marketer from Email Geeks indicates that receiving Mailbox Provider (MBP) specific average send rates per hour would be incredibly useful. This would need to consider the number of IPs in the sending mix to be accurate.

03 Sep 2019 - Email Geeks

Marketer view

Email marketer from Joe PR suggests that email marketing performance benchmarks, including open rates and click-through rates, are more indicative of success than raw sending speed, guiding optimization efforts.

22 May 2025 - Joe PR

What the experts say

Experts in email deliverability clarify that while Message Transfer Agents (MTAs) and ESP infrastructure possess high sending capacities, actual email delivery speed is predominantly dictated by the receiving Mailbox Providers (MBPs) and the sender's reputation. They underscore that ESPs intentionally manage sending rates to align with ISP connection limits and avoid triggering spam filters. The focus for high-volume senders should thus be on maintaining stellar sender hygiene and optimizing content, rather than solely on raw throughput figures which are often misleading.

Expert view

Expert from Email Geeks indicates that most ESP sending speed is intentionally limited by design. They follow best practices on how many emails to send to specific Mailbox Providers per hour or connection.

03 Sep 2019 - Email Geeks

Expert view

Expert from SpamResource highlights that email sender reputation is paramount. If reputation is low, ESPs are less likely to deliver emails to the inbox, often resulting in them landing in spam or being blocked.

10 Aug 2024 - SpamResource

What the documentation says

Official documentation and research often emphasize the technical foundations and best practices that govern email sending speeds. These sources consistently highlight the role of authentication protocols (SPF, DKIM, DMARC), IP reputation, and adherence to industry standards in ensuring efficient and reliable email delivery. While they may not provide explicit benchmarks for ESP sending speeds, they detail the mechanisms by which mailbox providers manage inbound email traffic, including throttling and connection limits. The underlying message is that speed is an outcome of good deliverability practices, not an isolated metric.

Technical article

Documentation from Customer.io indicates that any high-quality ESP should enforce proper domain authentication, comply with SMTP sending standards, and maintain specific ISP-level configurations to ensure reliable deliverability.

10 Apr 2023 - customer.io

Technical article

Documentation from Encharge.io explains that email reputation is influenced by various factors, including the sender's authentication setup, historical sending practices, and the overall quality of the email content.

15 Jun 2024 - Encharge

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