How many subdomains should I create for my email sending, and what naming conventions should I use?
Michael Ko
Co-founder & CEO, Suped
Published 18 Jul 2025
Updated 16 Aug 2025
7 min read
When managing email deliverability, a common question arises: how many subdomains should you create for your email sending, and what naming conventions are best? The decision to use subdomains, and how many, is critical for segmenting your email traffic and protecting your sending reputation. It allows for isolation, meaning that if one stream of email encounters issues (like a sudden increase in complaints), it won't necessarily tank the deliverability of your other, more critical email types.
Using subdomains is a widely accepted best practice, especially for businesses sending different types of emails, such as marketing newsletters, transactional alerts, or customer support communications. Each subdomain can develop its own unique sending reputation. This separation helps prevent a negative impact on your core domain's reputation if one email stream faces deliverability challenges, such as being placed on an email blacklist or blocklist.
While there's no strict limit on the number of subdomains you can create, the optimal number often depends on your specific sending needs, volume, and organizational structure. The key is to find a balance that provides sufficient isolation without introducing unnecessary complexity or diluting your sender reputation too much. This article explores how to determine the right number of subdomains for your operations and how to choose effective naming conventions.
Determining the right number
There isn't a hard limit to the number of subdomains you can create for your email sending. Many hosting providers and DNS services support a virtually unlimited number, constrained only by technical specifications like the 255-byte limit for a full hostname. However, practical considerations often dictate that fewer is better. Each subdomain requires proper configuration of DNS records, including SPF and DKIM, and often a DMARC record, increasing management overhead. For more information, see our guide on DNS lookups, SPF records, and subdomain usage.
The main reason to use multiple subdomains is to segment your email streams. This strategy helps isolate the reputation of different email types. For example, if your marketing emails face deliverability issues due to low engagement or high complaint rates, your critical transactional emails (like password resets or order confirmations) sent from a separate subdomain will remain unaffected. We often recommend starting with a minimum of two subdomains: one for transactional email and one for marketing email.
Beyond these two core categories, you might consider additional subdomains based on the complexity of your email program or organizational structure. For instance, if you have distinct lines of business, global regions, or specific platforms with their own email sending needs, more subdomains could be beneficial. However, avoid excessive fragmentation where individual subdomains do not send enough volume to build a reliable reputation. A good rule of thumb is to have at least 1,000 to 2,000 emails per month per subdomain to establish a consistent sending reputation.
The choice between a few well-managed subdomains and many highly specialized ones depends on your ability to monitor and maintain their individual reputations. Keep in mind that each subdomain you create adds to your ongoing management tasks, including blocklist monitoring and response, and consistent adherence to best practices for each sending stream.
Naming conventions for email subdomains
Choosing the right naming conventions for your subdomains is as important as deciding how many to create. Subdomain names should be descriptive, clear, and relevant to the type of email traffic they carry. This helps recipients recognize the sender and understand the nature of the email, contributing to better engagement and sender reputation. It also assists mail filtering systems in categorizing your mail correctly. For more details, explore our guide on selecting a subdomain for marketing emails.
Avoid generic or potentially misleading names. Names that might trigger spam filters, like 'spam.' or 'virus.', should be avoided at all costs. Similarly, using generic numeric names like 'email1.', 'email2.', etc., can make it harder to differentiate between email streams and manage their individual reputations effectively.
The M3AAWG (Messaging Malware and Mobile Anti-Abuse Working Group) recommends that the subdomain name should be relevant to the type of email traffic sent. For example, news.yourdomain.com for newsletters, trans.yourdomain.com for transactional messages, or alerts.yourdomain.com for notifications. This helps clarify the purpose of the email for both recipients and mail filters. Also, ensure you don't use another company's brand within your subdomain, even if you have a license to operate on their behalf. This can be seen as deceptive and may lead to deliverability issues, including being blocklisted.
A good naming convention should be easy to understand and remember, helping you and your team manage your email infrastructure more efficiently. Consider the types of emails you send and create names that accurately reflect their content or purpose.
Managing your subdomain strategy
Properly managing your subdomains is crucial for maintaining good email deliverability. Each subdomain needs to be authenticated correctly with SPF, DKIM, and DMARC. Regularly monitor the performance of each subdomain using tools like Google Postmaster Tools or email deliverability testers to spot any issues early. This proactive approach can help you prevent a subdomain from being blacklisted (or blocklisted) and mitigate any negative impact on your overall sending reputation.
When you introduce new subdomains, remember the importance of warming them up. This involves gradually increasing your sending volume over time to build a positive reputation with internet service providers (ISPs). Starting with low volumes and slowly scaling up helps ISPs recognize your subdomain as a legitimate sender, reducing the likelihood of your emails being flagged as spam. This process is crucial even if you are using shared IP pools.
Below is a comparison of typical scenarios for subdomain usage:
Scenario: Few subdomains
Often just two: marketing.yourdomain.com and trans.yourdomain.com.
Reputation Impact: Stronger reputation for each due to higher volume on fewer subdomains.
Ideal for
Small to medium businesses: With distinct transactional and marketing email streams.
Centralized sending teams: Where one team manages all email types.
Scenario: Many subdomains
Categorized by function, region, or department, e.g., billing.yourdomain.com, eu.yourdomain.com.
Disadvantages: Increased management complexity and potential for diluted reputation.
Reputation Impact: Reputation can be harder to build if volume per subdomain is too low.
Ideal for
Large enterprises: With diverse product lines or global, decentralized teams.
Specialized sending: For specific campaigns or highly sensitive email types.
Regularly reviewing your subdomain strategy is also important as your business evolves. What works today might not be optimal tomorrow. As sending volumes change or new email types emerge, you may need to adjust your subdomain structure to maintain optimal deliverability and protect your overall domain reputation.
Views from the trenches
Best practices
Clearly define the purpose of each subdomain (e.g., marketing, transactional, alerts) to simplify management and monitoring.
Segment your email traffic by type using subdomains, which helps isolate reputation issues and protect your primary domain.
Ensure that each subdomain has proper authentication (SPF, DKIM, DMARC) configured to validate its sending legitimacy.
Common pitfalls
Creating too many subdomains without sufficient sending volume can dilute sender reputation and make it harder to warm up effectively.
Using generic or misleading subdomain names (e.g., 'email1', 'spam') can negatively impact deliverability and trust.
Failing to warm up new subdomains gradually can lead to immediate deliverability issues and being flagged by ISPs.
Expert tips
For decentralized teams or global operations, consider subdomains based on region or distinct lines of business to maintain control and reputation.
If your organization has strict compliance or security requirements, additional subdomains might be necessary for specific, highly sensitive email streams.
Periodically review your subdomain strategy as your email program grows or changes, adjusting the number and naming conventions as needed.
Expert view
Expert from Email Geeks says there are no limits on the number of subdomains or naming conventions. However, each subdomain needs its own DKIM key to build an independent sending reputation. Segmenting different traffic types like transactional or marketing through subdomains is a best practice. A minimum volume, perhaps 1,000 to 2,000 emails per month, is needed to build a sending reputation.
2022-03-10 - Email Geeks
Marketer view
Marketer from Email Geeks says that while there's no technical restriction, they would avoid using subdomain names like 'virus.domain.com' or 'spam.domain.com'. It's also important not to overlook the process of warming up a new subdomain, even if it's on a shared IP pool.
2022-03-10 - Email Geeks
Striking the right balance
Deciding how many subdomains to create and what to name them is a strategic decision that impacts your email deliverability and management efficiency. There's no universal magic number; instead, it's about finding the right balance for your organization's specific needs. Prioritizing segmentation for different email streams, especially transactional versus marketing, is a strong starting point.
Always aim for descriptive and intuitive subdomain names that clearly indicate the email's purpose. This helps both recipients and filtering systems, leading to better inbox placement and improved email deliverability. Consistent monitoring and adherence to best practices for each subdomain will ensure a robust and resilient email sending infrastructure.
