How to set up email subdomains and what DNS records are required?
Michael Ko
Co-founder & CEO, Suped
Published 31 May 2025
Updated 14 Aug 2025
9 min read
Summary
Setting up email subdomains is a critical step for managing email reputation and ensuring deliverability, especially when sending different types of emails (e.g., marketing, transactional, operational). This process involves configuring specific DNS records for the subdomain, which allows mail servers to authenticate your emails and verify their legitimacy. Understanding the roles of various DNS records like SPF, DKIM, DMARC, and MX is key to a successful setup.
Key findings
Reputation isolation: Subdomains allow you to isolate the sending reputation of different email streams. If one stream (e.g., marketing emails) experiences deliverability issues, it won't negatively impact the reputation of other critical streams (e.g., transactional emails) sent from a separate subdomain.
DNS records are essential: Proper configuration of DNS records like SPF, DKIM, and DMARC is fundamental for email authentication and preventing your emails from being flagged as spam or rejected. An SPF record on a subdomain is generally required, while DKIM and DMARC records also play crucial roles.
MX record necessity: While an MX record is primarily for receiving mail, it can also be needed for subdomains used for sending, especially if bounce messages are directed back to the sending subdomain.
Domain registrar interface: The setup process largely depends on your domain registrar or DNS hosting provider's interface, but the underlying DNS record types remain consistent.
Key considerations
Comprehensive authentication: Ensure that all three key email authentication protocols (SPF, DKIM, DMARC) are properly configured for each sending subdomain to maximize deliverability and trust with receiving mail servers. You can learn more about DMARC, SPF, and DKIM setup.
A records for tracking: While not always strictly necessary for email sending, an A record might be required if your email service provider (ESP) uses the subdomain for tracking opens and clicks, pointing to their tracking servers.
Variations in ESP requirements: Different ESPs may provide slightly different sets of DNS records (e.g., CNAMEs for DKIM or tracking) specific to their infrastructure. Always refer to your ESP's documentation for precise instructions.
Email marketers often approach subdomain setup with a mix of familiarity and caution, acknowledging the critical role DNS records play in successful email campaigns. Many understand the concept but seek concrete steps or reassurance, highlighting the practical challenges of translating theoretical knowledge into actual configuration within diverse web hosting environments.
Key opinions
Seeking clarity: Many marketers, even those with some technical understanding, look for clear, step-by-step documentation on subdomain setup for specific email streams to ensure they cover all necessary bases.
Hosting provider dependency: The ease of setting up a subdomain and managing its DNS records is heavily dependent on the web-hosting provider's interface (e.g., cPanel) and tools.
Basic understanding: There's a common (and sometimes mistaken) belief that setting up an A record pointing to a sending IP is the primary or sole requirement for subdomain email sending, indicating a need for broader education on the full suite of necessary DNS records.
Reputation is key: Marketers understand the value of using subdomains to protect their main domain's reputation, especially when experimenting with new email strategies or managing different traffic types.
Key considerations
Verify DNS requirements: Marketers should always verify the specific DNS records (SPF, DKIM, DMARC, MX, CNAMEs for tracking) required by their chosen email service provider, as these can vary.
Utilize cPanel or similar tools: If using a web-hosting provider with a control panel like cPanel, marketers should familiarize themselves with its domain and DNS management sections, as these simplify the record addition process.
Understand the impact: Marketers should understand how each DNS record contributes to email authentication and deliverability, ensuring their messages reach the inbox and avoid blacklists (or blocklists). WP Mail SMTP provides a good overview of email subdomains.
Marketer view
Marketer from Email Geeks suggests that the process of setting up subdomains is heavily reliant on the specific web-hosting provider and their software, like cPanel. They recall cPanel making it quite easy, by simply navigating to the domain management menu to add the subdomain and then managing its records there.
30 Dec 2019 - Email Geeks
Marketer view
Email marketer from WP Mail SMTP emphasizes that using an email subdomain helps protect your primary domain's reputation. If one type of email, like marketing newsletters, experiences issues, it won't affect the deliverability of your transactional emails sent from your main domain or another subdomain.
22 Jan 2022 - WP Mail SMTP
What the experts say
Experts emphasize that email subdomain setup is more complex than just a simple A record. They stress the absolute necessity of multiple DNS record types for proper email authentication and deliverability, underscoring that without these, emails are highly likely to be rejected or land in spam folders. The technical nuances, like the distinction between records needed for sending versus tracking, are critical for successful implementation.
Key opinions
Beyond A records: Simply setting an A record for a subdomain pointing to an IP is insufficient for email sending. Comprehensive setup requires multiple other DNS entries, as an A record is not even essential for email sending.
Minimum record requirements: At a minimum, SPF (TXT), MX, and DKIM (TXT) records are typically needed for a sending subdomain. DMARC (TXT) might also be required, depending on whether it's handled at the organizational domain level or needs explicit subdomain configuration.
Additional records for functionality: Other records, such as A records for tracking (e.g., click and open tracking) or TXT records for verification with tools like Google Postmaster Tools, may also be necessary depending on the email setup.
Technical documentation is key: While technical, documentation like M3AAWG's sending domain best practices provides the foundational theory and setup guidance needed for correct configuration.
Key considerations
DMARC policy placement: Consider whether your DMARC policy for the subdomain should be explicitly defined or if it will inherit from the organizational domain. For best practices, review DMARC record placement for subdomains.
Zone file formatting: Understanding how a DNS zone file is formatted can help in accurately adding or modifying records for your subdomain, as improper syntax can lead to validation failures. Dyn's documentation provides details on how to format a zone file.
Troubleshooting: If initial setup fails, systematic troubleshooting of each DNS record, confirming correct values and propagation, is necessary. Using DNS lookup tools can help verify that your records are published correctly.
Long-term deliverability: Correct DNS configuration for subdomains is a foundational element for maintaining good email deliverability and avoiding blocklists (or blacklists) in the long term.
Expert view
Expert from Email Geeks states that an A record is not even necessary for sending emails, correcting the common misconception that it is a fundamental requirement for email subdomain setup. This highlights the importance of precise DNS configuration for email.
30 Dec 2019 - Email Geeks
Expert view
Deliverability expert from Spam Resource emphasizes that dedicated sending domains, which are typically subdomains, help manage reputation. They explain that separating different email streams prevents a single bad campaign from impacting the deliverability of all your email.
10 Apr 2024 - Spam Resource
What the documentation says
Official documentation from various sources, including M3AAWG and DNS service providers, provides detailed technical specifications and best practices for setting up email subdomains and their associated DNS records. It often outlines the precise format and purpose of each record, stressing adherence to standards for optimal interoperability and deliverability across the internet.
Key findings
M3AAWG recommendations: The M3AAWG provides comprehensive best practices for sending domains, often including detailed guidance on subdomains and their DNS requirements for various email functions, from sending to bounce handling.
Zone file structure: Documentation on zone files details how various DNS records (A, MX, TXT, CNAME) are structured and recorded within a domain's DNS settings, which is crucial for manual configuration.
Authentication standards: Official RFCs and related documentation define the specifics of SPF, DKIM, and DMARC, including their record types (always TXT) and how they must be published in DNS for successful authentication.
Domain registrar instructions: Many domain registrars provide specific instructions on how to add and manage subdomains and their DNS records within their unique control panels.
Key considerations
Complete record set: Ensure that for a sending subdomain, you configure not just SPF but also DKIM and DMARC, even if the DMARC policy for the root domain applies, to provide robust authentication. For more details, see what DNS records are needed for email sending subdomains.
Propagation time: After adding or modifying DNS records, allow sufficient time for changes to propagate across the internet, typically up to 48 hours, although it often happens much faster.
Verification tools: Utilize online DNS lookup tools to verify that your newly added subdomain records are correctly published and visible globally.
Avoid common pitfalls: Documentation often warns against common mistakes, such as having multiple SPF records on a single domain or exceeding the 10-lookup limit, which can lead to authentication failures. For more, read about best practices for DNS lookups and SPF records.
Technical article
Documentation from M3AAWG (Messaging, Malware and Mobile Anti-Abuse Working Group) outlines that a dedicated sending domain, often a subdomain, should be used for outbound email. This strategy helps to minimize the risk to the main domain's reputation if the sending practices lead to blocklisting (or blacklisting) or low reputation.
20 Dec 2019 - M3AAWG
Technical article
AWS documentation on configuring email servers states that for a subdomain, you need to choose the correct DNS record type for each entry. It lists common record types like A, MX, CNAME, and TXT, explaining that each serves a distinct purpose in email routing and authentication.
