Why do emails to .com domains send faster than other TLDs and what factors affect email sending speed?
Michael Ko
Co-founder & CEO, Suped
Published 14 Jul 2025
Updated 15 Aug 2025
7 min read
I've often heard discussions in the email community about how certain Top-Level Domains (TLDs) might impact email sending speed. Recently, during a large email send, I observed something interesting firsthand. When sending to a list composed almost entirely of .com domains, my completion rate was significantly faster compared to a broader list that included various other TLDs. For instance, in one hour, the .com-only list was 81% complete, while the mixed list was barely at 50%.
This observation raised an important question: Is there something inherently faster about sending to .com domains, or are other factors at play? It seems counterintuitive that a domain extension alone would dictate sending speed, so I started looking into the underlying mechanisms that govern how quickly emails are processed by recipient servers. The difference of just 20,000 emails on a list of 350,000 shouldn't cause such a drastic bottleneck if it were purely about volume.
My initial hypothesis leaned towards the composition of the .com list itself. A list predominantly composed of .com addresses is likely to contain a higher proportion of emails destined for major mailbox providers like Gmail, Yahoo, or AOL. These large providers have sophisticated infrastructures designed to handle massive volumes of incoming mail efficiently. This leads me to believe the perceived speed advantage isn't about the .com TLD itself, but rather the underlying server capabilities.
The role of DNS and connection setup
When an email is sent, the sending server must perform several actions before the message is accepted by the recipient's server. One of the initial steps is a DNS lookup to find the Mail Exchange (MX) records for the recipient's domain. These records tell the sending server which mail servers are responsible for accepting email for that domain.
Example DNS MX record lookupBASH
dig MX example.com
For major email providers, this DNS lookup is a one-time (or infrequent) operation for a multitude of recipients. When you send to many Gmail addresses, you're looking up Gmail's MX records once, then sending many emails to the same set of servers. This amortizes the setup costs, including DNS queries and establishing an SMTP session, across numerous messages. In contrast, if your list contains many obscure or unique domains, each might require a fresh DNS lookup and a new connection, adding latency.
The speed at which these DNS lookups and connection establishments occur can vary significantly. Large, well-maintained DNS infrastructure will respond quickly, while smaller, less robust setups might introduce delays. These cumulative delays become noticeable when processing hundreds of thousands of emails.
Receiver infrastructure and sender reputation
Beyond the initial DNS lookup, the speed at which emails are accepted heavily depends on the recipient mail server's infrastructure and the sender's reputation. Major mailbox providers like Google and Yahoo (and Microsoft) invest heavily in robust, high-capacity systems that can process millions of emails per hour. They are designed for rapid ingestion.
In contrast, smaller or independently hosted mail servers may have less sophisticated hardware, limited bandwidth, or stricter rate limits. They might simply not be able to accept emails as quickly, leading to deferrals and slower overall sending times. This difference in processing capability often correlates with the size and reputation of the domain. Large, well-known domains tend to use major providers, while niche TLDs or lesser-known domains might use smaller, less optimized services.
Sender reputation also plays a critical role in how quickly a mailbox provider accepts mail. If your sending IP or domain has a strong, positive reputation, providers are more likely to accept your mail at higher speeds. Conversely, a poor reputation can lead to throttling, temporary rejections (deferrals), or even outright blocking. While the TLD itself doesn't directly influence reputation, certain TLDs have been observed to be disproportionately associated with spam and phishing, which can lead to heightened scrutiny by ISPs, slowing down delivery to those TLDs. You can read more about how certain generic TLDs are used for spam in this analysis.
For example, sending to domains that frequently appear on email blocklists (or blacklists) will naturally slow down your campaigns, as recipient servers will often perform blocklist checks before accepting messages. Your overall email sending practices significantly impact your domain reputation and deliverability.
Major mailbox providers
Infrastructure: Highly optimized, high-capacity servers designed for rapid email ingestion.
Processing speed: Quick acceptance, minimal deferrals for good senders.
Reputation handling: Sophisticated filtering, but high volumes are expected and processed efficiently from reputable senders.
Smaller or niche domains
Infrastructure: Potentially less robust servers, limited bandwidth, or shared hosting environments.
Processing speed: Slower acceptance rates, more frequent deferrals, or aggressive throttling.
Reputation handling: May have stricter spam filters or less tolerance for high volumes from unfamiliar senders.
List hygiene and handling deferred emails
The composition of your email list and how you manage bounces and deferrals can significantly affect overall sending speed. If your list contains a large number of invalid, inactive, or slow-to-respond addresses, your sending system will spend more time attempting to deliver to them. Each failed attempt, timeout, or temporary rejection (deferral) adds to the processing time.
Many email sending systems are configured to retry delivery to deferred addresses multiple times over a set period. While this is a necessary feature for successful deliverability, an excessive number of retries can create bottlenecks and slow down the entire sending process. If your system isn't quickly pruning (or suppressing) addresses that consistently result in DNS timeouts or connection failures, these problematic recipients will continue to strain your sending resources.
This is why list hygiene is paramount. Regularly cleaning your email list to remove invalid or unresponsive addresses is crucial for maintaining efficient sending speeds and improving your overall deliverability. A smaller, cleaner list can often perform better and send faster than a larger list riddled with problematic addresses.
The hidden cost of uncleaned lists
A common pitfall I see is overlooking the impact of even a small percentage of problematic email addresses. While 20,000 emails out of 350,000 might seem minor, if these are frequently deferring or causing timeouts, they can disproportionately slow down your entire send. Your system wastes resources attempting to deliver to these addresses, leading to extended queue times for legitimate messages. Ensuring good email sending speed practices is essential.
Optimizing your email sending speed
The observation about .com domains sending faster is likely a reflection of the email ecosystem rather than an inherent property of the TLD itself. It highlights the importance of understanding not just your sending infrastructure, but also the characteristics of your recipient list and the behavior of various mailbox providers. By optimizing your DNS lookups, maintaining a clean list, and understanding how different receiving domains operate, you can significantly improve your email sending speed and deliverability.
Effective email deliverability isn't just about avoiding the spam folder, it's also about efficient message delivery. Paying attention to these technical nuances, from DNS resolution to recipient server responsiveness, can make a tangible difference in the performance of your email campaigns. Additionally, familiarizing yourself with how TLD choice impacts email deliverability can provide further insights, though the direct speed impact is often secondary to reputation and infrastructure.
Views from the trenches
Best practices
Optimize your DNS configuration to ensure quick MX record lookups and efficient connection establishments.
Segment your lists by dominant TLDs (or rather, by major mailbox providers) to tailor sending speeds and avoid throttling.
Regularly clean your email lists to remove unresponsive or invalid addresses, reducing deferrals and improving efficiency.
Implement a system that quickly prunes (or suppresses) addresses causing repeated DNS timeouts or connection failures.
Common pitfalls
Assuming all TLDs are equal in terms of recipient server infrastructure and processing capabilities.
Overlooking the cumulative latency introduced by DNS lookups and connection setup for a diverse range of smaller domains.
Failing to remove hard bounces or continually retrying emails to non-existent or perpetually deferred addresses.
Not monitoring queue times and delivery statuses per domain to identify specific bottlenecks in your sending.
Expert tips
Use per-MX distribution analysis of your recipient list to understand where your emails are primarily going.
Leverage advanced logging to identify domains that are consistently slow to accept mail or cause high deferral rates.
Consider warming up new sending IPs and domains gradually, especially when targeting less common TLDs.
Ensure your email authentication (SPF, DKIM, DMARC) is correctly configured to build and maintain a strong sender reputation.
Expert view
Expert from Email Geeks says that if a list is mostly Gmail, Yahoo, and Hotmail/Outlook, those providers are designed to accept large volumes of email quickly, which could explain faster send times for a .com heavy list. This makes the observation about .com TLDs being faster a coincidence, rather than a rule.
2020-12-30 - Email Geeks
Expert view
Expert from Email Geeks says that performing several DNS lookups for each unique domain is a high-latency operation. However, for major providers, you only do this once or a few times for many recipients, which makes the process more efficient.
Gmail, 
Yahoo
, or 
AOL. These large providers have sophisticated infrastructures designed to handle massive volumes of incoming mail efficiently. This leads me to believe the perceived speed advantage isn't about the .com TLD itself, but rather the underlying server capabilities.
