How to create sender email addresses for new subdomains in an ESP?

Key findings

• ESP control: Most ESPs manage the creation of sender email addresses and aliases directly within their platform once a subdomain is properly authenticated, negating the need for IT to create each individual address.
• Initial IT setup: The critical step requiring IT involvement is the initial setup of DNS records, such as TXT or CNAME records, to delegate the subdomain to the ESP. This authentication confirms the ESP is authorized to send email on your behalf for that specific subdomain.
• MX records: For inbound mail to the subdomain (e.g., replies), a separate MX record may be required. This record tells the internet where mail for that subdomain should be delivered, either back to your internal mail infrastructure or managed by the ESP, depending on your setup. Refer to our guide on how to add an MX record to a subdomain.
• ESP variation: The exact steps can vary between ESPs. Always consult your ESP's specific documentation for precise instructions on subdomain setup and sender address creation.

Key considerations

• Delegation strategy: Decide whether the subdomain will be entirely relegated to the ESP for all mail handling or if inbound mail needs to be routed internally. This choice impacts DNS record configuration.
• Authentication methods: Understand the authentication methods your ESP supports (TXT, CNAME, etc.) for verifying subdomain ownership. For more on this, read our simple guide to DMARC, SPF, and DKIM.
• Future flexibility: Consider the long-term implications of subdomain delegation, especially if you plan to use multiple ESPs or change providers in the future. Email subdomains are essential for deliverability segmentation.
• Internal communication: Maintain clear communication with your IT and security teams regarding DNS changes and subdomain usage to ensure smooth setup and avoid deliverability issues.

Key opinions

• ESP-driven setup: Marketers frequently express the belief that most of the work for sender address creation happens within the ESP's interface, assuming the subdomain itself is already configured.
• Confusion on creation: There can be initial confusion about how a new email address, like hello@email.segment.com, is 'created' if it's not a traditional mailbox, highlighting a gap in understanding between marketing and IT perspectives.
• Authentication as key: Marketers recognize that authenticating the subdomain with the ESP's TXT records (or other DNS entries) is the fundamental prerequisite before any sender addresses can be used. This is a critical step for good sender reputation.
• Independence post-setup: Many marketers anticipate being able to create multiple sender aliases independently within their ESP once the initial subdomain authentication is complete, without further IT tickets per alias.

Key considerations

• Naming conventions: Think strategically about the sender email addresses (e.g., hello@, support@, marketing@) used for different types of emails (transactional, marketing, support) to maintain clarity and brand consistency. For best practices, see our article on using single versus multiple email sender addresses.
• Deliverability impact: Understand that using a branded sending domain or subdomain with proper authentication significantly improves email deliverability and sender reputation. Choosing the right sender email address is crucial for newsletters and transactional emails.
• Reply-to addresses: Ensure that reply-to addresses are correctly configured to receive responses, whether they are managed by the ESP or routed back to an internal mailbox.
• ESP instructions: Always prioritize the specific setup instructions provided by your ESP, as configurations can vary widely.

Key opinions

• ESP delegation: Experts generally agree that once a subdomain is fully delegated to an ESP, the ESP is responsible for managing sender addresses on it.
• MX record nuance: MX records are crucial for inbound mail to the subdomain. If the subdomain is entirely relegated to the ESP for sending, the MX record might still need to point to internal mail infrastructure for replies, or the ESP might manage it if they handle inbound email as well.
• CNAME implications: If using a CNAME for subdomain aliasing, experts point out that the responsibility for publishing the inbound MX record might rest with the domain owner, not necessarily the ESP. This is important for reverse DNS resolution and overall deliverability.
• Varying ESP solutions: The specific solution for setting up sender addresses can vary significantly between different ESPs, necessitating direct consultation with the ESP's documentation or support.

Key considerations

• DNS record accuracy: Ensure all DNS records (TXT, CNAME, MX) are correctly configured as per your ESP's instructions. Errors here can lead to email deliverability issues and impact your sender reputation.
• Inbound vs. outbound: Clearly distinguish between records needed for outbound sending (SPF, DKIM handled via ESP's TXT/CNAME) and inbound replies (MX record). These are distinct but equally important for comprehensive email management.
• Subdomain purpose: Consider the specific purpose of the new subdomain. Using a dedicated subdomain for marketing emails, for example, helps isolate the reputation from your main domain and other email functions. Read more on why use subdomains for email marketing deliverability.
• ESP-specific guidance: Always defer to your specific ESP's documentation and support for definitive answers on their implementation of subdomain and sender address creation. This is paramount, as expert advice often highlights the variability between providers.

Key findings

• DNS record creation: Documentation from ESPs like Mailgun and Klaviyo explicitly states that you need to add specific DNS records (CNAME, TXT) to your domain's DNS settings to verify ownership of the subdomain. This is the initial setup phase.
• Sender address within ESP: Many ESPs' guides imply or explicitly state that once the domain/subdomain is verified, you can then add and manage sender email addresses (the 'From' address) directly within their platform's interface. These are not separate mailboxes in the traditional sense.
• Authentication protocols: Documentation often details how CNAME delegation enables critical authentication protocols like SPF and DKIM for email sending, which are vital for deliverability.
• Branded sending: Documentation consistently emphasizes the benefits of setting up a branded sending domain or subdomain for better control over sender reputation and brand appearance in the inbox.

Key considerations

• DNS propagation time: Be aware that DNS changes can take time to propagate across the internet, impacting when your subdomain and sender addresses become fully operational. This can take a few hours up to 48 hours.
• Clear instructions: Follow your ESP's step-by-step instructions precisely. Missing a record or misconfiguring one can lead to authentication failures and affect your email deliverability. For example, some ESPs require MX records for subdomains.
• Subdomain purpose: Ensure the subdomain serves its intended purpose. For instance, a subdomain used for email marketing (mail.yourcompany.com) should be distinct from a subdomain for a blog (blog.yourcompany.com). More details can be found in documentation about what an email subdomain is and why use one.
• Authentication verification: ESPs typically provide tools to verify that your DNS records are correctly set up, which should be utilized before attempting to send. This aligns with guidelines on how SPF, DKIM, and DMARC affect deliverability.