Should I send email from a client's primary domain or a subdomain?
Michael Ko
Co-founder & CEO, Suped
Published 19 May 2025
Updated 17 Aug 2025
8 min read
When sending emails on behalf of a client, a common question arises: should you use their primary domain (e.g., clientdomain.com) or a dedicated subdomain (e.g., mail.clientdomain.com)? This decision significantly impacts email deliverability and sender reputation, especially with the latest Gmail and Yahoo requirements. It's a critical discussion, particularly when clients push back on using subdomains, often due to a misunderstanding of email technicalities. Let's explore the implications of each approach.
Understanding email sending domains
The choice between a primary domain and a subdomain for email sending primarily concerns how your emails are authenticated and how their reputation is managed. A primary domain, also known as a root or apex domain, is the main web address for a business. A subdomain is a prefixed extension of that primary domain, often used to organize different parts of a website or, in this case, different email streams.
From a technical standpoint, email authentication protocols like SPF, DKIM, and DMARC rely on DNS records associated with the sending domain. When you send an email, two domains are typically involved: the Header From domain (what recipients see) and the Envelope From domain (also known as the Return-Path or Bounce Address, used for SPF checks and bounce processing). For proper authentication and deliverability, these domains, or their associated subdomains, must be correctly configured.
Using a subdomain for email is a common practice because it allows for granular control over email reputation. Different subdomains can be used for different types of email, like marketing messages versus transactional notifications. This separation can prevent issues with one email stream from negatively affecting others associated with the primary domain.
Reputation management and isolation
One of the most compelling reasons to use a subdomain for sending client emails is sender reputation management. Your sender reputation is a crucial factor in whether your emails reach the inbox or end up in the spam folder. When you send from a primary domain, all email streams originating from that domain share the same reputation. If one stream performs poorly (e.g., high bounce rates, spam complaints), it can negatively impact the deliverability of all other emails sent from that domain.
A subdomain, on the other hand, allows for reputation isolation. By dedicating a specific subdomain (e.g., marketing.clientdomain.com or news.clientdomain.com) for bulk or marketing emails, you create a distinct sending identity. This means that if marketing emails encounter deliverability issues, the reputation of the client's main domain, used for essential transactional or corporate communications, remains largely unaffected.
This isolation is particularly beneficial for agencies. It protects the client's core business email activities from the potential risks associated with large-scale sending, such as hitting spam traps or being placed on an email blacklist (or blocklist). It also provides a buffer, minimizing the impact of any deliverability challenges on your other clients or your own sending reputation.
Sending from a primary domain
Shared reputation: All email streams on the same domain contribute to a single, overarching sender reputation. A negative impact from one stream, such as marketing emails, can affect the inbox placement of critical transactional messages.
Higher risk profile: Increased risk of the primary domain being flagged by internet service providers (ISPs) or added to a blocklist (or blacklist) if email practices are suboptimal. This can lead to widespread deliverability issues for all email traffic from that domain.
Sending from a subdomain
Reputation isolation: Different email types (e.g., promotional, transactional) can operate on separate subdomains, each building and maintaining its own distinct reputation. This protects the primary domain's reputation from potential issues.
Lower risk exposure: If deliverability issues arise on a specific subdomain (e.g., due to a marketing campaign), the impact is confined to that subdomain, preserving the integrity and performance of the client's main email domain.
Email authentication and compliance
Email authentication is non-negotiable for modern deliverability. Both primary domains and subdomains can be configured with SPF and DKIM records to verify sender identity. For SPF, the record must be associated with the Envelope From domain (Return-Path), which often defaults to a subdomain of your email service provider (ESP) or a dedicated client subdomain. For DKIM, the d= tag in the signature must align with the Header From domain or a subdomain of it for DMARC alignment.
Many clients might initially suggest simply adding your ESP's SPF records to their main domain. However, this is usually not the correct approach. SPF records should be specific to the domain used in the Return-Path header. If your ESP uses a subdomain for its return path, SPF would need to be configured for that specific subdomain, not the client's primary domain directly. The client's primary domain can still be used in the visible From header for branding purposes, while the technical sending happens via a properly authenticated subdomain, ensuring DMARC alignment.
Example SPF record for a subdomainDNS
v=spf1 include:_spf.mailgun.org ~all
The latest Google and Yahoo requirements for bulk senders underscore the importance of proper authentication. They mandate DMARC policies, aligned SPF, and aligned DKIM. While there might be anecdotal reports about certain domain types (like .org or educational domains) not yet seeing full enforcement, this is not a permanent exclusion. The rollout of these policies is ongoing, and compliance will eventually be expected across the board to ensure email security and combat spam. Relying on an apparent temporary leniency is a risky strategy for long-term deliverability.
Addressing client concerns and misconceptions
Clients often resist using subdomains because they believe it dilutes their brand identity. They want their emails to visibly come from their primary domain, which is entirely understandable from a marketing perspective. The key is to explain that a subdomain for technical sending does not prevent the use of their primary domain in the friendly From header. For example, an email can display as 'Your Company <info@clientdomain.com>' while technically being sent via 'mail.clientdomain.com'.
It's important to clarify that no domain types are excluded from the new email authentication requirements. Whether a domain ends in .com, .org, .edu, or any other top-level domain, the expectation for proper SPF, DKIM, and DMARC configuration applies. Any perceived grace period for specific domain types is temporary and should not be relied upon for a robust deliverability strategy.
Educating clients about these nuances is crucial. Frame the use of subdomains not as a limitation, but as a proactive measure to safeguard their main domain's reputation and ensure consistent inbox delivery for all their email communications. Emphasize that adopting best practices now will prevent more severe deliverability issues in the future. This approach helps build trust and positions your agency as an expert in email security and deliverability.
Strategic choices for email senders
For agencies and bulk senders, the strategic choice almost always leans towards using a client's subdomain for email sending. This isn't just about technical compliance, but also about maintaining distinct reputations and minimizing risk. When you send emails on behalf of multiple clients, isolating each client's sending reputation on a dedicated subdomain becomes even more critical.
While it's technically possible to authenticate emails for a primary domain directly, it often complicates DNS management and creates a single point of failure for reputation. If a client's overall email practices are not meticulous, their primary domain could suffer, impacting all their internal and external communications. By using a subdomain, you provide a clear boundary, ensuring that your campaigns' performance doesn't inadvertently harm the client's broader email ecosystem.
Feature
Primary domain (clientdomain.com)
Subdomain (mail.clientdomain.com)
Sender reputation
Shared across all email traffic, high risk of collateral damage.
Isolated per email stream, mitigates reputation risk for primary domain.
Authentication (SPF/DKIM)
Requires careful management to avoid conflicts with existing records.
Easier to configure dedicated DNS records without interfering with primary domain.
Branding
Directly uses the main brand name in the 'From' header, strong immediate recognition.
Can still use primary domain in 'From' header, subdomain handles technical sending.
Complexity for clients
Perceived as simpler, but can lead to more complex troubleshooting later.
Requires understanding of subdomain benefits; initial setup may seem more complex.
Views from the trenches
Best practices
Always use the client's domain for sending, even if it's a subdomain, to clearly represent the correct brand and avoid confusion.
Utilize subdomains for the Envelope From (Return-Path) and configure SPF for that specific subdomain to ensure proper authentication.
Educate clients that using a subdomain for technical sending does not prevent their primary domain from appearing in the friendly From header.
Common pitfalls
Do not add an Email Service Provider (ESP) directly to the main domain's SPF record as it authenticates the Return-Path domain, not the visible From header.
Relying on assumptions that certain domain types like .org or educational domains are exempt from new email authentication requirements, as enforcement is ramping up for all.
Sharing reputation across all email streams by sending marketing and transactional emails from the same primary domain, which can risk collateral damage.
Expert tips
If a client's ESP supports primary domain authentication, it's technically possible to send from it, but consider the broader implications for shared reputation.
DMARC alignment can be achieved by using the main domain in the From header while configuring SPF and DKIM on a subdomain.
For optimal setup, configure SPF and DKIM for a subdomain and then use that subdomain for the Return-Path while maintaining the primary domain in the friendly From header.
Expert view
Expert from Email Geeks says: Educational and .org domains are not excluded from standard email authentication protocols like DMARC.
April 16, 2024 - Email Geeks
Marketer view
Marketer from Email Geeks says: The new email sending rules apply to .org domains, and enforcement has been actively increasing since February.
April 16, 2024 - Email Geeks
Making the right choice for your client
While clients may prefer the simplicity and immediate brand recognition of using their primary domain, advocating for a subdomain for email sending is a professional and responsible choice for any agency or email sender. It aligns with current best practices for email deliverability and provides crucial protection for the client's overall sender reputation.
By understanding and clearly communicating the technical intricacies and long-term benefits of subdomain usage – particularly in terms of reputation isolation and compliance with evolving email standards – you can guide your clients toward a strategy that ensures optimal inbox placement and safeguards their brand's digital communications. Ultimately, a properly configured subdomain is an investment in resilient and effective email delivery.
Google and 
Yahoo requirements for bulk senders underscore the importance of proper authentication. They mandate DMARC policies, aligned SPF, and aligned DKIM. While there might be anecdotal reports about certain domain types (like .org or educational domains) not yet seeing full enforcement, this is not a permanent exclusion. The rollout of these policies is ongoing, and compliance will eventually be expected across the board to ensure email security and combat spam. Relying on an apparent temporary leniency is a risky strategy for long-term deliverability.
