What are the common technical hurdles when using one subdomain for multiple ESPs?

While it's technically feasible to add multiple SPF mechanisms to include different platforms, and use different DKIM selectors, you can run into conflicts, especially with CNAME records that different platforms might require. It's often more complex to manage than setting up a new subdomain.

Can using the same subdomain for different platforms hurt my overall sender reputation?

Yes, it can. If one platform sending from the shared subdomain engages in practices that harm sender reputation (e.g., high spam complaints), it can negatively affect the deliverability of emails sent by all other platforms sharing that subdomain, as reputation is tied to the domain (or subdomain).

What are the benefits of using separate subdomains for each email sending platform?

The primary benefit is reputation isolation. If one email stream or platform experiences a deliverability issue, it won't impact others. This makes troubleshooting easier and protects your critical email communications from being affected by less critical ones, such as cold outreach.

How difficult is it to set up a new, dedicated subdomain for a different email platform?

This setup is relatively simple. You'll need to create a new subdomain in your DNS provider and then configure the SPF, DKIM, and DMARC records specifically provided by the new email sending platform for that unique subdomain. This ensures a clean and conflict-free setup.

Can I use the same subdomain for multiple email sending platforms? - Sender reputation - Email deliverability - Knowledge base

The question of whether you can use the same subdomain for multiple email sending platforms is a common one, and the short answer is yes, technically, you often can. However, the longer, more nuanced answer involves understanding the potential complexities and risks. While it might seem convenient to consolidate, there are critical considerations that can impact your email deliverability and overall sender reputation.

Many email service providers (ESPs) require specific DNS records to authenticate your sending domain (or subdomain), including SPF, DKIM, and DMARC. When you introduce a second platform to the same subdomain, you risk creating conflicts with these records, which can lead to email authentication failures and ultimately, messages landing in the spam folder or being blocked entirely.

Understanding subdomains and email authentication

A subdomain is a unique extension of your main domain (e.g., mail.yourdomain.com). They are commonly used for email sending because they allow you to separate different email streams, protecting your main domain's reputation. Each email sending platform you use needs to authenticate that it is authorized to send emails on behalf of your subdomain. This authentication relies heavily on proper DNS records.

For instance, SPF (Sender Policy Framework) records specify which mail servers are authorized to send email from your domain. DKIM (DomainKeys Identified Mail) uses digital signatures to verify the sender and ensure message integrity. DMARC (Domain-based Message Authentication, Reporting, and Conformance) builds on SPF and DKIM to provide a policy framework for how recipients should treat emails that fail authentication. These records are crucial for your messages to reach the inbox, as explored in articles like A simple guide to DMARC, SPF, and DKIM.

When multiple platforms attempt to send from the same subdomain, they each require their unique authentication keys and records to be published in your DNS. While SPF allows for multiple included mechanisms to authorize different sending sources, DKIM usually requires distinct selector records for each sending system. For example, one DKIM record might be s1._domainkey.yourdomain.com for one platform, and s2._domainkey.yourdomain.com for another. Understanding these requirements from each provider is the first crucial step.

Example of an SPF record including multiple platformsDNS

v=spf1 include:spf.marketo.com include:spf.crowdtech.com ~all

DNS conflicts and deliverability implications

The primary challenge with sharing a subdomain stems from potential DNS conflicts. While SPF records can generally accommodate multiple include mechanisms, some ESPs require CNAME records for authentication that might clash with each other if not carefully managed. A CNAME record, or Canonical Name record, maps an alias name to a true domain name. You cannot have two different CNAME records for the exact same hostname.

Another significant concern is bounce handling. When emails bounce, the sending platform needs to process these bounces to maintain list hygiene. If you have two platforms sending from the same subdomain, it becomes complex to ensure each platform receives and processes only its relevant bounces. Mismanaged bounces can negatively affect your sender reputation and increase your chances of being placed on an email blacklist (or blocklist).

Additionally, DMARC alignment becomes more intricate. For DMARC to pass, the domain in the From header must align with the domain authenticated by SPF or DKIM. If different platforms use different authentication methods or domains in the Return-Path or DKIM signatures, ensuring consistent DMARC alignment across all sending streams from a single subdomain can be a headache. You can read more about the nuances of shared subdomains and reputation risks in our article, Risks of using the same sending domain on multiple IPs.

Single subdomain shared

DNS records: Requires careful merging of SPF records. Potential for DKIM or CNAME conflicts. Each platform must support flexible DNS setup for shared usage.
Reputation impact: Issues from one platform (e.g., spam complaints or a blocklist event) can negatively affect the sending from all other platforms sharing the subdomain. This makes isolating and fixing deliverability problems much harder.
Bounce handling: Complex to manage bounce data across multiple systems if they all point to the same return-path. Incorrect handling can lead to poor list hygiene.
Deliverability visibility: It becomes difficult to pinpoint which platform is causing deliverability issues when all emails originate from the same reputation pool.

Dedicated subdomain per platform

DNS records: Each platform has its own set of distinct SPF, DKIM, and DMARC records, simplifying configuration and avoiding conflicts.
Reputation impact: Reputation is isolated to each subdomain. A problem with one platform won't affect the deliverability of emails sent from another, protecting your overall email program.
Bounce handling: Each platform processes its own bounces, simplifying data management and ensuring accurate suppression lists. This is critical for maintaining good sender health.
Deliverability visibility: Clear visibility into the performance of each sending stream, allowing for targeted optimization and faster troubleshooting.

Reputation and deliverability risks

Sender reputation is built over time based on various factors, including bounce rates, spam complaint rates, and engagement. When multiple platforms share the same subdomain, their sending behaviors are inextricably linked under that one subdomain's reputation. If one platform sends to a low-quality list or has a sudden spike in complaints, it can negatively impact the deliverability of emails sent from the other platform, even if that second platform is performing well. This is why email subdomains are often recommended.

To mitigate this risk, it is common practice to segregate different types of email streams, such as marketing emails, transactional emails, and cold outreach, onto distinct subdomains. This approach helps to isolate reputation issues. For instance, if your marketing emails experience a deliverability problem, your critical transactional emails (like password resets or order confirmations) sent from a different subdomain remain unaffected. This is a key reason why many email experts advocate for using email subdomains for different purposes.

A shared subdomain also complicates the process of monitoring and troubleshooting. If you observe a sudden drop in inbox placement rates, it can be challenging to determine which sending platform (and its associated practices) is the root cause. Without clear separation, diagnosing and fixing issues becomes a much more complex and time-consuming task, potentially leading to prolonged deliverability problems and lost revenue.

Risks of sharing subdomains

When you use the same subdomain for multiple email sending platforms, you intertwine their sender reputations. This means that poor sending practices from one platform, such as high bounce rates, spam complaints, or being caught by a spam trap, can directly impact the deliverability of emails sent by all other platforms sharing that subdomain. This shared risk can lead to:

Reduced inbox placement: Emails from all platforms might end up in spam or get blocked.
Difficulty in troubleshooting: Pinpointing the exact source of a deliverability issue becomes challenging.
Brand reputation damage: A blocklist event on one platform impacts all email sent from that subdomain, affecting trust in your brand.

Recommended approach: dedicated subdomains

Given the complexities and potential risks, the most robust and recommended approach is to use separate, dedicated subdomains for each email sending platform or for distinct email streams (e.g., marketing, transactional, cold outreach). This strategy ensures that each subdomain builds and maintains its own sender reputation, isolating any issues to a specific stream or platform. For more best practices on using subdomains, you can refer to Best practices for using unique or shared email subdomains.

Setting up an additional subdomain is typically a straightforward process. It involves creating a new subdomain (e.g., research.yourdomain.com) and then configuring the specific SPF, DKIM, and DMARC records that your new email sending platform provides. This ensures that each platform has its own dedicated authentication path, minimizing conflicts and improving overall deliverability. While there's an initial setup effort, it's generally far less complex than troubleshooting intricate DNS conflicts or recovering from a damaged sender reputation.

By adopting a dedicated subdomain strategy, you gain better control over each email stream's deliverability, make troubleshooting much simpler, and protect your primary domain's reputation. It's a proactive measure that strengthens your overall email program's resilience and effectiveness. Remember, the goal is to ensure your emails reach the inbox consistently, and proper subdomain management is a cornerstone of that objective.

Best practices for multiple platforms

Dedicated subdomains: Assign a unique subdomain for each email sending platform you use. This isolates reputation and prevents DNS conflicts.
Segment email types: Even within a single platform, consider using different subdomains for different email types (e.g., transactional, marketing, cold outreach). For guidance, see Should I use separate subdomains for different email types.
DMARC monitoring: Implement DMARC for all subdomains and monitor your reports. This provides visibility into authentication failures and potential issues.
Provider documentation: Always consult your ESP's documentation for their specific DNS requirements and recommendations.

Views from the trenches

Best practices

Always use dedicated subdomains for different sending platforms to avoid DNS conflicts and isolate reputation.

Segment email streams (marketing, transactional) onto separate subdomains to protect your primary domain's reputation.

Thoroughly review each ESP's DNS authentication requirements before setup to prevent future issues.

Implement DMARC with a monitoring policy to gain visibility into authentication failures across all your sending subdomains.

Common pitfalls

Attempting to share the same CNAME record across multiple email providers, which is technically impossible.

Failing to account for unique bounce handling mechanisms when sharing subdomains, leading to poor list hygiene.

Not considering the impact of a blocklist event on one shared platform affecting all other email streams.

Underestimating the complexity of managing SPF, DKIM, and DMARC alignment for shared subdomains.

Expert tips

Map out your entire email sending ecosystem and plan your subdomain strategy carefully from the outset.

Regularly monitor your domain and IP reputation using tools like Google Postmaster Tools.

Ensure that all sending platforms are correctly configured for DMARC alignment to prevent deliverability issues.

For small volume senders, consider if branded authentication is even necessary for a secondary platform.

Marketer view

Marketer from Email Geeks says that sometimes there are reconcilable DNS record conflicts that make using the same subdomain impossible.

2020-07-22 - Email Geeks

Marketer view

Marketer from Email Geeks notes that custom authentication often requires specific CNAMEs or TXT records, which can conflict if not managed properly.

2020-07-22 - Email Geeks

The path to optimal deliverability

While it is technically possible to use the same subdomain for multiple email sending platforms, it's generally not the recommended approach due to the significant risks it poses to your email deliverability and sender reputation. The potential for DNS conflicts, complex bounce handling, and intertwined reputations can lead to serious issues, including increased spam placement and even being added to a blocklist.

Opting for dedicated subdomains for each platform or email stream offers a much more robust and manageable solution. This strategy simplifies DNS configuration, isolates reputation, streamlines troubleshooting, and ultimately ensures your emails reliably reach their intended recipients. Prioritizing a well-structured subdomain strategy is a foundational step towards achieving excellent email deliverability.