What are the risks of using the same sending domain on multiple email platforms and IPs?
Matthew Whittaker
Co-founder & CTO, Suped
Published 30 Apr 2025
Updated 19 Aug 2025
8 min read
Many organizations use a single sending domain across various email platforms and IP addresses for different types of communication, such as marketing, transactional, or operational emails. While this might seem efficient, it introduces significant risks to your email deliverability and overall sender reputation. I've seen countless instances where this approach leads to unforeseen complications, impacting inbox placement and email effectiveness.
The core issue boils down to how Internet Service Providers (ISPs) and mailbox providers like Gmail and Outlook assess sender reputation. They evaluate both your IP reputation and your domain reputation, and these can influence each other, sometimes in detrimental ways. If one IP or platform experiences issues, it can quickly cascade and affect the reputation of your entire sending domain, pulling down the deliverability of otherwise healthy email streams.
This can make it challenging to diagnose and remediate deliverability problems. Understanding the nuances of how these reputations interact is crucial for maintaining strong sender status and ensuring your emails reach their intended recipients. It is also important to consider if sending from multiple systems affects deliverability.
The interplay of IP and domain reputation
When you use the same sending domain across multiple IP addresses, particularly from different email platforms, you create a complex web of interactions that can impact your sender reputation. While IP reputation is tied to the specific server sending the email, domain reputation is associated with your brand and is often weighted more heavily by major mailbox providers. This distinction is critical because a poor IP reputation can still drag down a good domain reputation.
For instance, a new IP address used for sending might not have established enough sending volume or a consistent positive sending history. This can cause emails sent from that IP to go to spam folders while the IP builds its reputation. If this new, less reputable IP shares the same sending domain as an established, high-reputation IP, the issues of the new IP can reflect negatively on the entire domain. Google recommends ideally sending all messages from the same IP address, or using different IPs for different message types if multiple are necessary.
This interplay means that the actions on one IP (e.g., high bounce rates, spam complaints) can affect the deliverability of emails sent from other IPs, even if those other IPs have excellent sending practices. It's like a chain where one weak link can compromise the strength of the whole. This is especially true for B2B sending, where each mailbox provider and spam filter maintains its own reputation assessments.
Authentication challenges
Email authentication protocols like SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting & Conformance) are fundamental to email security and deliverability. When using multiple platforms and IPs with the same sending domain, managing these records becomes significantly more complex. Each platform or IP needs to be authorized to send on behalf of your domain.
An SPF record, for example, lists all authorized IP addresses and sending sources for your domain. If you add too many includes (lookups) from different platforms to your SPF record, you risk exceeding the 10 DNS lookup limit. Exceeding this limit causes SPF authentication to fail, leading to emails being rejected or sent to spam.
SPF record complexity
Managing multiple SPF records or a single complex SPF record for various sending services is challenging. Exceeding the 10 DNS lookup limit is a common issue that will cause SPF validation failures. This can significantly hurt your email deliverability.
Example of an SPF record including multiple servicesDNS
DKIM and DMARC also require careful configuration across all platforms. Misaligned or incorrectly configured DKIM and DMARC records can lead to emails failing authentication checks, increasing the likelihood of them being marked as spam or rejected outright. Without proper email authentication, even legitimate emails can struggle to reach the inbox.
The dangers of mixed mail streams
When different types of email, such as marketing blasts and critical transactional notifications, are sent from the same domain and potentially mixed IP pools, it creates a 'mixed mail stream'. This can be highly problematic for deliverability. Marketing emails often have lower engagement rates and higher complaint rates compared to transactional emails, which are usually highly anticipated by recipients.
If your marketing emails, sent from one IP, generate a high volume of spam complaints or low engagement, the overall reputation of your sending domain can suffer. This negative reputation then impacts your crucial transactional emails, sent from a different IP but the same domain, causing them to land in spam folders or be blocked. It's a significant risk because even a small margin of complaints can significantly damage your domain reputation.
This scenario can lead to your domain being placed on an email blocklist (also known as a blacklist). Many blocklists are triggered by unsolicited emails, poor list hygiene, or malicious emails. Once your domain is on a blocklist, it becomes exceedingly difficult to reach the inbox, impacting all email streams from that domain, regardless of their content or purpose. Recovering your domain reputation from a blacklist can be a lengthy process.
Risks of mixing streams
Reputation contamination: Poor performance from one email stream (e.g., marketing) can negatively impact the deliverability of all other streams, including critical transactional emails.
Blacklist risk: Higher spam complaint rates from one IP or platform could lead to your entire sending domain being placed on a blocklist (blacklist).
Difficult troubleshooting: Pinpointing the source of deliverability issues becomes harder when multiple platforms and IPs share a single domain.
Benefits of separation
Reputation firewall: Using subdomains creates a separation, protecting your primary domain's reputation from the potentially lower reputation of other streams.
Improved deliverability: Each stream can build its own positive reputation, leading to better inbox placement across the board.
To mitigate these risks, I strongly recommend separating your email streams by using subdomains. Instead of sending all emails from example.com, consider using marketing.example.com for promotional content, transactional.example.com for alerts, and so on. This creates a 'reputation firewall' where the reputation of one subdomain does not directly contaminate another. This is particularly effective for mailbox providers who weigh domain reputation highly.
Each subdomain can then have its own dedicated IP address or set of IPs and proper authentication records (SPF, DKIM, DMARC) configured for its specific sending platform. When introducing new IPs or subdomains, remember to follow a careful IP warm-up process to build a positive sending history gradually. This involves starting with low volumes and slowly increasing them over time, ensuring consistent positive engagement. This also applies when considering if you can use the same subdomain for multiple email platforms.
Monitoring the deliverability and reputation of each subdomain independently is key. Utilize tools to track metrics like bounce rates, spam complaint rates, and inbox placement for each stream. This proactive approach allows you to identify and address issues within a specific mail stream before they compromise your entire brand's email reputation. Remember, consistency and careful management are your best allies in email deliverability.
Views from the trenches
Best practices
Use distinct subdomains for different email streams, such as marketing, transactional, and operational communications.
Implement proper SPF, DKIM, and DMARC records for each subdomain to ensure authentication passes consistently.
Carefully warm up new IP addresses and subdomains by gradually increasing sending volume and monitoring engagement.
Continuously monitor the reputation of each subdomain and its associated IPs using deliverability tools and Postmaster Tools.
Segment your email lists carefully and maintain high list hygiene to minimize bounces and spam complaints.
Common pitfalls
Using a single sending domain across multiple email platforms can lead to reputation contamination from one problematic IP.
Exceeding the 10 DNS lookup limit in SPF records by including too many third-party services.
Failing to properly configure DKIM and DMARC for all sending sources, resulting in authentication failures.
Mixing high-volume, low-engagement marketing emails with critical transactional emails on the same domain/IPs.
Neglecting to warm up new IP addresses, leading to immediate spam folder placement or blocks.
Expert tips
Consider using dedicated IPs for high-volume or critical email streams to gain more control over your sending reputation.
Regularly review your DMARC reports to identify authentication failures and unauthorized sending sources.
Focus on maintaining consistent sending volumes and patterns for each IP to build a stable reputation.
Educate your team on email sending best practices to avoid common mistakes that can hurt deliverability.
For B2B sending, pay close attention to how new IPs perform with G Suite and Office 365, as their filters are rigorous.
Marketer view
Marketer from Email Geeks says if you are B2C, Gmail primarily cares about domain reputation.
2019-06-26 - Email Geeks
Expert view
Expert from Email Geeks says if you are using two unique IPs from two different ESPs, you should use different subdomains.
2019-06-27 - Email Geeks
A strategic approach to multi-platform sending
While using the same sending domain across multiple email platforms and IP addresses might seem convenient, the risks to your email deliverability and sender reputation are substantial. The intertwined nature of IP and domain reputation means that issues with one part of your sending infrastructure can easily contaminate the entire domain, leading to emails landing in spam or being blocked.
The complexity of managing email authentication protocols like SPF, DKIM, and DMARC across diverse sending environments, coupled with the dangers of mixed mail streams, necessitates a more strategic approach. Separating your email traffic onto different subdomains is a best practice that establishes a crucial reputation firewall. This allows each email stream to build and maintain its own distinct reputation, safeguarding your brand's overall email integrity.
Ultimately, proactive management, diligent monitoring, and adherence to email sending best practices are essential. By strategically organizing your sending infrastructure, you can mitigate risks, improve inbox placement, and ensure your messages consistently reach your audience, regardless of the platform or IP used.
Gmail and 
Outlook assess sender reputation. They evaluate both your IP reputation and your domain reputation, and these can influence each other, sometimes in detrimental ways. If one IP or platform experiences issues, it can quickly cascade and affect the reputation of your entire sending domain, pulling down the deliverability of otherwise healthy email streams.
