Should I use the same or different subdomains for multiple ESPs?
Matthew Whittaker
Co-founder & CTO, Suped
Published 16 Jul 2025
Updated 15 Aug 2025
5 min read
When managing email marketing and transactional communications, many organizations use multiple Email Service Providers (ESPs). A common question arises regarding how to set up your sending domains, specifically whether to use the same subdomain across all ESPs or opt for distinct ones. This decision has significant implications for your sender reputation, deliverability, and overall email program management.
The choice isn't always straightforward, as both approaches have benefits and drawbacks depending on your specific sending volume, email types, and risk tolerance. Understanding how subdomains affect your sender reputation and deliverability is key to making the best decision for your email strategy.
Understanding sender reputation and subdomains
Your sender reputation is crucial for email deliverability. It's essentially how mailbox providers view your sending practices and trustworthiness. This reputation is tied to your domain and IP address. When you use subdomains, they inherit reputation from the root domain, but they also build their own specific reputation based on the mail sent through them.
A key concept here is reputation isolation. If you send different types of emails (e.g., marketing, transactional, cold outreach) from distinct subdomains, a negative reputation event on one subdomain, such as high spam complaints from a marketing campaign, is less likely to severely impact the deliverability of emails sent from another, like your critical transactional emails. This segregation protects your most important email streams.
ESPs typically guide you on how to set up your DNS records, including SPF and DKIM, for the sending domains or subdomains you choose. Properly configured DNS records are fundamental for email authentication, which in turn influences your sender reputation. For a comprehensive overview, consider reviewing an article about the basics of email subdomains.
The case for distinct subdomains
Opting for distinct subdomains for each ESP or even for different email streams within the same ESP offers several advantages. The primary benefit is the ability to isolate sender reputation.
Distinct subdomains
Reputation isolation: A problem with one email stream (e.g., promotional emails via promo.yourdomain.com) is less likely to affect the deliverability of another (e.g., transactional emails via mail.yourdomain.com).
Tailored sending practices: You can optimize each subdomain's sending strategy according to its specific email type and ESP's recommendations, like segmenting email streams.
Simplified DMARC alignment: It can be simpler to ensure DMARC alignment for each subdomain, as each ESP will provide specific instructions for their setup, as opposed to configuring the implications of sharing a subdomain between two ESPs.
Single (same) subdomain
Brand consistency: All emails appear to come from a single, unified source, reinforcing your brand identity.
Simplified DNS management: Fewer DNS records to maintain, reducing the potential for configuration errors.
Consolidated reputation: A strong positive reputation built through one ESP can potentially benefit emails sent via another using the same subdomain.
Many industry experts and organizations, including M3AAWG, strongly recommend assigning a separate subdomain for each distinct sending purpose. This practice is particularly vital for protecting critical email streams from the potential fallout of less stringent marketing campaigns.
The case for a single (same) subdomain
While distinct subdomains are generally recommended for risk mitigation, there can be arguments for using a single subdomain across multiple ESPs. This approach is often considered for maintaining a unified brand presence or when managing DNS records is a significant concern.
Risk of shared reputation
Using a single subdomain (or the same sending domain) for multiple ESPs means that the sender reputation is shared more intensely. If one ESP or one type of email stream experiences deliverability issues (e.g., high spam complaints, bounces, or blacklist appearances), it can negatively impact all email sent from that same subdomain, regardless of which ESP sent it. This shared reputation can be problematic if your ESPs handle different types of email with varying levels of risk.
While simplified DNS management is an attraction, the potential deliverability risks often outweigh this benefit for organizations serious about email performance. It's crucial to weigh the convenience against the potential for significant deliverability challenges, including emails going to spam.
Technical considerations for multiple ESPs
Regardless of whether you choose the same or different subdomains, proper technical configuration of your DNS records is non-negotiable. This includes setting up SPF, DKIM, and DMARC. Each ESP will provide specific records you need to add to your DNS, and these will differ based on whether you're using a shared or distinct subdomain.
Example SPF record for a single subdomain across multiple ESPsDNS
It's important to differentiate between your From: address and the domain used for email authentication (SPF and DKIM). While the From: address should be consistent for brand recognition and replies, the underlying authentication domains can, and often should, vary. For example, DMARC reports should typically go to an automated service rather than your main reply-to email address.
High risk of blocklisting. Full isolation is often needed to protect your main brand. This is a critical factor for building your sending reputation.
Monitoring your domain and IP reputation using tools like Google Postmaster Tools is essential, regardless of your subdomain strategy. This helps you quickly identify any negative trends and take corrective action before they severely impact deliverability.
Views from the trenches
Best practices
Always align your authentication domains (SPF/DKIM) with your From: header for DMARC.
Use distinct subdomains for different email types, such as transactional and marketing.
Ensure DMARC reports (rua/ruf) go to an automated monitoring service, not your reply-to address.
Regularly monitor your domain and IP reputation with tools like Google Postmaster Tools.
Common pitfalls
Using the same subdomain for high-risk (e.g., cold outreach) and critical (e.g., transactional) emails.
Not having DMARC alignment between the From: header and authentication domains.
Sending DMARC reports to an email address that isn't regularly monitored or is intended for human replies.
Failing to configure proper SPF, DKIM, and DMARC records for each ESP and subdomain.
Expert tips
If using multiple ESPs, ensure each has its own unique set of authentication records on your distinct subdomains.
Consider a phased approach when migrating or adding ESPs, carefully monitoring deliverability at each step.
Always maintain separate subdomains for critical email streams to prevent reputation bleed from marketing or bulk sends.
Even if DMARC alignment is not essential to pass deliverability checks, it's a strong goal for robust email security.
Expert view
Expert from Email Geeks says the decision to use the same or different subdomains depends on whether you want your mail streams to more strongly share their reputation.
2021-01-05 - Email Geeks
Expert view
Expert from Email Geeks says you ideally want your mail authenticated via both SPF and DKIM, with DMARC alignment to the From: header, though it's not strictly essential for deliverability.
2021-01-05 - Email Geeks
Making the right choice for your email program
For most organizations using multiple ESPs, the recommended best practice is to use different subdomains for each ESP, or at least for distinct types of email (e.g., transactional versus marketing). This strategy helps to isolate sender reputation, mitigating the risk of one ESP's performance or a problematic email campaign negatively impacting your overall deliverability.
While using a single subdomain might seem simpler from a DNS management perspective, the potential for shared negative reputation often outweighs this convenience. Prioritizing deliverability and sender reputation health means segmenting your email streams with dedicated subdomains and ensuring robust authentication for each, allowing you to maintain high inbox placement rates for all your critical communications.
