How does sending internal system notifications affect transactional email deliverability when using the same ESP?
Matthew Whittaker
Co-founder & CTO, Suped
Published 8 Aug 2025
Updated 19 Aug 2025
8 min read
Many businesses use the same email service provider (ESP) for all their sending needs, from crucial transactional emails to internal system notifications. While this might seem efficient, it raises an important question: does sending low-engagement internal notifications affect the deliverability of high-priority transactional emails, especially when using the same ESP?
The short answer is yes, it can. Email deliverability relies heavily on sender reputation, which is influenced by various factors, including recipient engagement. When internal system notifications, often sent in high volume to a concentrated domain like Gmail (if your internal emails are on Google Workspace), receive low opens or high bounces (due to inactive employee accounts), it can negatively impact the overall sender reputation of your domain and IP address. This, in turn, can affect the deliverability of your critical transactional emails.
While it might not be a catastrophic impact instantly, it introduces a risk that can degrade your deliverability over time. Understanding how different email streams interact on the same sending infrastructure is crucial for maintaining optimal inbox placement.
The intertwined nature of sender reputation
Sender reputation is the cornerstone of email deliverability. Internet Service Providers (ISPs) like Yahoo and Microsoft continuously evaluate your sending practices to determine if your emails are legitimate or spam. This evaluation often happens at the IP and domain level. If your transactional emails and internal notifications share the same IP address and sending domain, their reputations are intertwined. A dip in one can pull down the other. You can find out more about this process in a guide on factors that affect email deliverability.
Transactional emails, by nature, are expected to have high engagement rates because they are triggered by user actions (e.g., order confirmations, password resets). Internal system notifications, on the other hand, might have lower engagement due to their administrative nature, or if they are sent to inactive accounts of former employees. When an ESP sees low open rates, high bounce rates, or even spam complaints from one stream, it impacts the overall perception of your sending domain and IP. This is similar to how throttled marketing sends can slow down transactional placement rates if IPs are shared.
IP reputation and domain reputation are distinct yet interconnected. While an ESP might manage the IP reputation, your domain’s reputation is largely in your hands. If unwanted internal notifications lead to a poor domain reputation, all emails sent from that domain, regardless of their purpose, can face deliverability challenges, including being sent to spam folders or being blocklisted (or blacklisted).
Risk factors from internal notifications
A primary concern with internal notifications is the potential for high bounce rates, especially if your system continues to send emails to addresses of former employees. Hard bounces (when an email address no longer exists) severely damage sender reputation. Similarly, if employees simply ignore or delete these notifications without opening them, it signals low engagement to ISPs, which can lead to filtering.
Moreover, internal system notifications might sometimes resemble spam to automated filters, especially if they contain generic alerts or lack clear personalization, even though they are legitimate within your organization. This can increase the likelihood of them being flagged, which then affects the overall deliverability of your domain, including your crucial transactional messages. Maintaining a clean recipient list is vital for good deliverability, and this applies to internal lists just as much as external ones.
Importance of list hygiene
Even for internal communications, a clean and active recipient list is paramount. Regularly remove email addresses of departed employees or those who no longer need these notifications. High bounce rates from any mail stream can signal to ISPs that your sending practices are poor, potentially leading to your IP or domain being put on a blocklist (or blacklist). Ignoring this can undermine your entire email program. Learn more about how email blacklists actually work.
Consider the impact of spam traps. While less common for internal emails, if old employee addresses are recycled into spam traps, sending to them can significantly damage your sender reputation. It's crucial to manage your internal recipient list diligently.
Strategies for insulation and improvement
The most effective way to mitigate this risk is to separate your email streams. This means sending transactional emails and internal system notifications from different subdomains and, ideally, different IP addresses. By doing so, the reputation of one stream does not directly impact the other. For instance, you could send transactional emails from mail.yourdomain.com and internal notifications from alerts.yourdomain.com. This segregation allows ISPs to evaluate each stream independently. We cover this in more detail in our article on separating marketing and transactional emails.
Beyond subdomains, consider using different DKIM selectors for each mail stream. While your ESP might send all mail from a shared IP pool, having distinct authentication (DKIM) for each type of mail helps mail servers recognize them as separate entities, even if the primary domain is the same. This can provide a layer of insulation for your transactional email reputation.
For your internal notifications, implementing robust list hygiene practices is non-negotiable. Regularly audit your recipient list to remove inactive or invalid employee email addresses. This reduces hard bounces and prevents sending to potentially unengaged or non-existent accounts, which bolsters your sender reputation across the board. Automating this process can significantly reduce manual effort and improve accuracy.
Combined sending
Reputation risk: Low engagement from internal notifications can directly degrade the deliverability of transactional emails due to shared IP/domain reputation.
Filtering: ISPs may apply the same filtering rules to all email types if the streams are not differentiated.
Complexity: Troubleshooting deliverability issues becomes harder as it's difficult to pinpoint which stream is causing the problem.
Segregated sending
Reputation insulation: Poor performance of one stream does not significantly impact the other, preserving transactional email deliverability.
Optimized delivery: Each stream can be optimized for its specific purpose and audience, leading to better overall inbox placement.
Clearer troubleshooting: Issues can be identified and resolved for a specific stream without affecting others.
Monitoring and authentication
Even with separation, continuous monitoring of your email deliverability metrics is essential. Pay close attention to open rates, bounce rates, and spam complaint rates for both your transactional and internal notification streams. Tools like ESPs and their rate limits can affect deliverability, so understanding your ESP's nuances is also key.
Utilize postmaster tools provided by major mailbox providers, such as Google Postmaster Tools, to gain insights into your sender reputation, IP reputation, and filtering rates. This data can help you identify if your internal notification stream is indeed causing issues and allow you to take corrective action promptly. Monitoring for blocklist (or blacklist) appearances is also critical. Learn how to recover your domain reputation if it takes a hit.
For setting up separate subdomains, you'll need to configure DNS records. Here's an example of how you might set up transactional.yourdomain.com and internal.yourdomain.com with your ESP.
DNS records for separate subdomainsDNS
transactional.yourdomain.com. IN CNAME mailgun.org.
dkim._domainkey.transactional.yourdomain.com. IN TXT "v=DKIM1; k=rsa; p=YOUR_DKIM_KEY_FOR_TRANSACTIONAL"
internal.yourdomain.com. IN CNAME mailgun.org.
dkim._domainkey.internal.yourdomain.com. IN TXT "v=DKIM1; k=rsa; p=YOUR_DKIM_KEY_FOR_INTERNAL"
Finally, ensure all your email streams are properly authenticated with SPF, DKIM, and DMARC. Even if internal notifications have lower engagement, strong authentication helps verify their legitimacy to receiving servers. You can explore our guide on DMARC, SPF, and DKIM for a comprehensive overview of these crucial protocols.
Proactive steps for deliverability
Factor
Impact on deliverability
Mitigation strategy
Shared IP/domain reputation
Poor engagement from one stream affects all, leading to spam filtering or blocklisting.
Separate email streams using subdomains, dedicated IPs, or distinct DKIM selectors.
High bounce rates
Sending to invalid addresses damages sender reputation and signals poor list hygiene.
Unopened emails signal to ISPs that content is unwanted, leading to lower inbox placement.
Review the necessity and content of internal notifications. Ensure they are valuable and relevant.
Authentication issues
Weak or misconfigured SPF, DKIM, or DMARC can lead to emails being rejected or sent to spam.
Ensure all email streams are properly authenticated and monitored. Consider separate authentication.
Ultimately, the choice to separate email streams depends on the perceived risk and current deliverability performance. If your transactional emails are landing in the inbox without issues, a gradual plan for segregation might be sufficient. However, if you're experiencing deliverability problems, isolating your high-priority transactional emails should be a more immediate priority to protect their crucial path to the inbox. It is also important to consider that identical practices on different platforms will yield similar deliverability results over time.
Views from the trenches
Best practices
Establish separate subdomains for transactional and internal notification emails.
Implement strong and distinct authentication (SPF, DKIM, DMARC) for each mail stream.
Maintain rigorous list hygiene for internal notification recipients by promptly removing inactive or departed employee email addresses.
Regularly monitor deliverability metrics like open rates, bounce rates, and spam complaints for all email streams.
Utilize postmaster tools from major ISPs to gain detailed insights into your sending reputation.
Common pitfalls
Using the same IP and domain for both high-engagement transactional emails and low-engagement internal notifications.
Failing to remove inactive or departed employee email addresses from internal notification lists, leading to high bounce rates.
Overlooking low open rates or spam complaints for internal notifications, which can drag down overall sender reputation.
Neglecting proper email authentication (SPF, DKIM, DMARC) for all sending streams, making it harder for ISPs to trust your mail.
Not segmenting email streams by content type, leading to a blended reputation that is difficult to manage and optimize.
Expert tips
Consider using a different ESP entirely for internal notifications if they are consistently impacting transactional email performance, especially if the volume is high or engagement is particularly low.
Automate the process of cleaning internal employee email lists by integrating with HR systems or directory services to ensure timely updates.
If complete separation is not immediately feasible, focus heavily on improving the engagement and list hygiene of your internal notifications as a first step.
Regularly review the content and necessity of internal notifications. Could some be consolidated or delivered through an alternative channel to reduce email volume?
For large organizations, creating dedicated shared IP pools for different mail streams within the same ESP can offer an additional layer of isolation, if your ESP supports it.
Expert view
Expert from Email Geeks says that deliverability depends on whether Google recognizes the mail streams as different, suggesting distinct DKIM 'd=' tags as a way to explicitly signal separation.
2020-03-13 - Email Geeks
Expert view
Expert from Email Geeks says that poor handling of internal campaigns, even if it only affects internal notifications, should be fixed because if the emails are worth sending in high volume, they are worth delivering.
2020-03-13 - Email Geeks
Key takeaways
Sending internal system notifications through the same ESP and from the same domain/IP as your transactional emails can indeed impact deliverability. The primary risk stems from the potential for lower engagement and higher bounce rates from internal communications, which can drag down your overall sender reputation. This intertwined reputation can lead to your critical transactional emails being filtered, delayed, or sent to spam.
While immediate catastrophic impact is unlikely, a proactive approach is always best. Implementing strategies such as using separate subdomains, distinct authentication methods, and rigorous list hygiene for your internal notifications can effectively insulate your transactional email deliverability. Continuous monitoring of your sender reputation and key email metrics will provide the insights needed to maintain healthy deliverability across all your email streams.
Gmail (if your internal emails are on 
Google Workspace), receive low opens or high bounces (due to inactive employee accounts), it can negatively impact the overall sender reputation of your domain and IP address. This, in turn, can affect the deliverability of your critical transactional emails.
Yahoo and 
Microsoft continuously evaluate your sending practices to determine if your emails are legitimate or spam. This evaluation often happens at the IP and domain level. If your transactional emails and internal notifications share the same IP address and sending domain, their reputations are intertwined. A dip in one can pull down the other. You can find out more about this process in a guide on factors that affect email deliverability.
