January 24, 2022

How Top Level Domain (TLD) Choice Impacts Email Deliverability

We've analysed and ranked the best to worst TLDs for email Deliverability

How Top Level Domain (TLD) Choice Impacts Email Deliverability

Introduction to TLDs impacting deliverability

There’s a trend where high performing demand generation teams are now using multiple email domains to separate cold outreach from their companies day to day business email domain. This means different top-level domains (TLDs) (email endings) are being used on the email accounts that conduct cold outreach compared to the ones which engage with customers. For example, we at Allegrow use a .co domain to communicate with current customers and a .net domain (amongst others) on our cold outreach. 

The reason marketers are adopting this approach is to keep the domain reputation that they use for cold outreach separate from the domain which they use for other operations like customer support, finance and general communications. This approach also has the added benefits of making the email domain that gets used for sales outreach easier to monitor, control and change/alternate if necessary so that the sales team can have the best possible deliverability due to a higher sender reputation

While having a separate domain for cold outreach (and potentially having multiple domains depending on the volume you conduct) is completely logical and generally considered best practice for teams that utilise cold email - this means that marketing and technology teams need to source and maintain different TLDs….When picking a new domain specifically for the purpose of outreach campaigns it’s important to be aware that some TLDs are more likely to land in spam folders than others. So you’ll want to make sure you don’t pick a secondary TLD which is starting at a disadvantage from the perspective of email deliverability. 

Using our ability to access data in thousands of active B2B spam folders, we’ve analyzed which TLDs are the safest bet to choose vs which appear to be more associated with spam. In order to make this a fair study, we have cross-referenced the frequency with which a specific TLD appears in spam folders against its general popularity. Through our report, we’ll highlight specific TLDs which are outliers on this basis and others that are exactly in line with expectations. 

Table of contents:

What is a Top-Level Domain (TLD)?

Deliverability vs Inbox Placement

The choices of Top-Level Domains for email (Ranked List)

Why would TLD choice impact deliverability? 

The Good - overperformed in comparison to their popularity

The Bad - negative outliers compared to their popularity

The Consistent  -  predictable and likely to be safe options

Which domains are best for Email Deliverability?

What is a Top-Level Domain (TLD)?

A Top-Level Domain, often abbreviated as TLD, is essentially the final part of your domain and the aspect of your web address that is not specific to your business name. For example, with our top-level domain is ‘.Co’. 

Specifically, in the context of email, when we’re referring to your domain we’re referencing whatever is written on your email address after the @ symbol appears. 

There are hundreds of different TLDs available to register and Kinsta explains more broadly the different categories of TLDs that are available. Within our report, we have used data from Namecheap to identify domains in a ranked list based on their registration popularity. 

Deliverability vs inbox placement

Deliverability is what marketers generally use to refer to the percentage of the emails they send which reach the customers on their list. However, the high-level number that is reported inside your marketing automation system can be misleading unless you also consider inbox placement in your analysis. 

Typically to calculate deliverability the following calculation is run:

$$ Deliverability = {Emails Sent-Bounced Emails \over Emails Sent}*100 $$

The flaw in the assumption above is assuming that an email which doesn’t bounce, is always delivered correctly. However, in many cases, (usually ranging from 10-50% of the time) emails are delivered to the spam folder or an unfocused folder where the recipient in question doesn’t check emails. 

Therefore, monitoring open and click rates on your emails as well as bounce rates provides an overall view of your email deliverability allowing you to optimize your approach for primary inbox placement. 

The choices of Top-level domains for email (Ranked List)

The general popularity of TLDs below have been verified (using Namecheap rankings as a data source). The reputation/deliverability ratings have been calculated by cross-referencing the frequency of TLDs appearing in spam folders against their popularity using data from Allegrow’s network including thousands of live emails addresses and active spam folders.

*Good - as the reputation value for a TLD indicates there was not a notable bias towards this TLD being present in spam folders compared to its popularity. 

*Bad - as the reputation value indicates the TLD in question was a considerable outlier by appearing in spam folders more frequently than would be expected compared to its popularity. 

*Unknown - indicates there was no notable trend/conclusive data of the domain in question landing in spam more or less often compared to its popularity. 

Why would TLD choice impact deliverability? 

Email providers are consistently looking to create a better experience for their users and searching for ways to easily identify, filter and hide emails that waste users time. This can be highlighted by around 28% of the worlds total email traffic being categorised as spam (which is around 85 billion emails per day being filtered away from recipients). 

In order to carry out this filtering, ISPs create reputation scores using AI to predict the likelihood that an email user will want to engage with a message. This score takes into account multiple aspects such as; the general engagement your specific domain receives over email, content and spam reports.

When you consider that people running spamming and phishing campaigns ‘churn and burn’ many different domains it’s common they (a) generally purchase multiple names at the same TLD for one campaign (due to bulk purchasing in batches) and (b) generally pick cheap TLDs for registration. This means that some TLDs are more commonly associated with spam emails compared to others. Our study of comparing the general popularity of a TLD  alongside how frequently emails using that TLD are found in spam folders is designed to help you avoid the worst performing TLDs and highlight the best options for email deliverability.

The Good - Overperformed in comparison to their Popularity

.io domain

The .io domain is primarily used inside the technology industry and has risen to be the 4th most common domain to register according to Namecheap. During analysis we found this domain being the 10th most common domain to find in spam folders. Therefore, this comparison would serve as an indication that the .io domain currently outperforms expectations in terms of deliverability and is a viable option. (As a note: to be consistent with our expectations this domain would have needed to be the 4th most common inside spam folders, however, seeing as this domain was less commonly found in spam folders it’s an outlier and placed inside our ‘Good’ category). 

.Org domain

While the .org domain is the 3rd most popular at registration this domain is the 5th most common TLD to be found in spam folders. This indicates that the .Org domain performs better than we expected and can be considered as part of the Good category. However, considering our data-set of spam folders is B2B this could be the reason for the lower than anticipated presence in spam folders (as businesses generally come into contact with non-profit domains less than consumers). Therefore, we’d advise although this domain is suggested to be a high performer according to our data set that unless the .org domain fits well with your business model then it may not be the best fit in terms of relevance. 


The .ca domain is the 9th most common at registration while this domain does not appear in the top 10 most popular domains we found in spam folders. This could be linked to the stricter privacy regulations in Canada (CASL legislation), meaning that Canadian run domains are less likely generally to be associated with spam. However, you should note with this TLD there are strict registration requirements that could make this domain a bad fit for your business.

*Remember nothing in this article is legal advice and please consult your legal counsel to ensure compliance with all relevant legislation. 

.Me domain

With .me being the 10th most common domain to register while not being inside the top 10 most common TLDs to be found in spam folders, the data suggests this domain has a good rating for deliverability. This domain has the intended use of companies being connected to Montenegro, while being popularly used for its personal connotations. 

.ai domain

Even though .ai is the 6th most popular domain at registration the .ai domain was not present inside the top 10 most common domains that we found in spam folders. This indicates general overperformance for deliverability. The domain is usually associated with companies focused on artificial intelligence projects. 

.dev domain

The .dev domain was the 9th most popular domain at registration, however, it did not appear inside the top 10 most common domains we found in spam folders. This could be due to the domain in question mainly being associated with development environments (which skews its registration popularity), which means although this domain is technically outperforming where we’d expect it, still wouldn’t be our first choice. 

The Bad - Negative Outliers compared to their popularity


The TLD .Buzz is not defined as one of the top 10 most popular domains to register. However, this TLD was the 6th most common domain to find in spam folders across the data set we measured. Therefore, this data suggests that the .Buzz TLD has a significant pre-disposition to be placed inside spam folders and/or is consistently used for spamming. Therefore, we’d recommend staying clear of the .Buzz TLD in the context of email marketing. 


The .Ph domain is not among the 10 most popular domains to register, while it was the 7th most common domain to find in spam folders out of the 515 TLDs we search for across thousands of active spam folders.

.Fr domain

We identified this domain as the 4th most common to be found in spam folders while the domain is not included in the top 10 most popular registration domains.

.Club domain

Not inside the 10 most common domains to register, while being the 9th most common domain to find in spam folders. Therefore, we’d advise not considering the .Club TLD as an option for your secondary TLDs.

The Consistent  -  Predictable and likely to be safe options

.Com domain

The .Com TLD is of course the most popular domain to register and exactly as you would expect the most common TLD to find in spam folders. Although this may not sound reassuring, the consistent trend which is shown by this analysis would suggest .Com is a safe choice for a TLD that will not negatively affect your deliverability purely due to the choice of the domain ending. The only issue with selecting this as a secondary TLD is it’s fairly likely your primary TLD is already a .com one. 

.Net domain

The .Net domain is the 2nd most popular at registration and 2nd most popular in spam folders, which implies this TLD is a safe choice for a secondary TLD in the context of email deliverability. There is also the added benefit with the .Net domain that you are more likely to find a .Net domain available compared to the alternative of the .Com domain. 

.Co Domain

The .Co TLD is 5th most popular at registration and 4th most common in spam folders. We would advise the difference in this trend of only 1 place can still be interpreted as a consistency. The likely explanation for the increase of the presence of this domain inside our dataset compared to general registration popularity is due to the fact we analysing a B2B dataset and as this is a commercial domain it’s likely to be one of the most common.

The domain was the 7th most common at registration and the 8th most commonly found in spam folders. Therefore, as this domain is within 1 position of where we’d expect it to rank, we believe this indicates the domain has consistent performance and would not cause any notable deliverability decline compared to another domain due to the choice of TLD. 

Which domains are best for Email Deliverability?

We’d advise, based on the analysis, that you should choose a TLD from either the list of consistent or good TLDs. Now after looking into the analysis for each TLD on these lists we’d summarise the best choices are the following: Com, .Net, .Co,, .io, .Ca, .Me and .ai. 

While considering these options it’s important to look into the registration requirements of any domain and keep in mind how closely the TLD in question relates to your business operations, for example, if your business is not related to AI in any way the .ai domain is likely a poor choice. 

For transparency, the dataset we’re using to analyse the presence of these TLDs in spam folders is consistently growing in line with the Allegrow network and we’ll update our findings to maintain and improve the accuracy of our report.