What are the best practices for email sending domains and IP reputation in business partnerships?
Michael Ko
Co-founder & CEO, Suped
Published 30 Jun 2025
Updated 19 Aug 2025
5 min read
Navigating email sending domains and IP reputation within business partnerships is crucial for maintaining strong deliverability. When two entities collaborate and share sending responsibilities, the email practices of one can directly influence the inbox placement and sender reputation of the other. My goal is always to ensure that every email sent reaches its intended recipient, and in a partnership, this requires careful strategic planning to prevent unforeseen deliverability challenges.
The primary concern in such scenarios is often how to segment sending activities to mitigate risk. For instance, if one partner is sending marketing emails that might generate higher complaint rates, you wouldn't want those to negatively impact the transactional emails that are critical to business operations. Understanding the nuances of domain and IP reputation, and how they interact, becomes paramount.
This involves careful consideration of domain delegation, IP allocation, and the implementation of robust authentication protocols to ensure both parties can send reliably without undermining each other's email standing.
Strategic subdomain usage for risk mitigation
When engaging in business partnerships that involve shared email sending responsibilities, a fundamental principle is the strategic use of subdomains. This approach helps isolate sending reputations, protecting the core brand domain from potential issues arising from a partner's email activity.
For example, if your company acts as a backend platform for a partner, sending transactional emails on their behalf, it's generally advisable to use a dedicated subdomain like wine.theirbrand.com rather than their primary domain. This way, if any deliverability challenges arise from the transactional emails (e.g., high bounce rates or spam complaints), only the subdomain's reputation is affected, leaving the main domain's reputation intact.
Many email service providers (ESPs) support delegating a subdomain for this purpose, making it a standard and recommended configuration. This separation ensures that one partner's email practices, whether good or bad, do not directly compromise the deliverability of the other's core communications.
It's important to remember that domain reputation is portable. This means that if you establish a strong reputation on a specific subdomain, that positive standing can be maintained even if you change IP addresses. In contrast, IP reputation is tied to the specific IP address used for sending.
Managing IP addresses in collaborative environments
Dedicated IP addresses
Provide granular control over your sending reputation. Your sending behavior is the sole determinant of your IP's standing. They are ideal for high-volume senders who can maintain consistent sending patterns.
Start small: Begin with low sending volumes to highly engaged subscribers.
Gradual increase: Slowly increase volume and recipient list size over time. A common strategy suggests adding around 20% more emails each day until the full volume is reached.
Monitor engagement: Pay close attention to open rates, click-through rates, and complaint rates during the warming phase.
Shared IP addresses
Distribute sending reputation across multiple senders using the same IP. This can be beneficial for low-volume senders, as they benefit from the collective positive reputation of other reputable senders on the shared IP. For high-volume senders or those with inconsistent sending practices, shared IPs can be risky.
Risks include being affected by the poor sending habits of others sharing the IP, potentially leading to deliverability issues even if your own practices are good. To mitigate this risk, many ESPs actively monitor and manage their shared IP pools.
Managing shared IPs in partnerships
Vet your ESP: Choose an ESP with a strong reputation for managing its shared IP addresses effectively.
Volume considerations: If a partner's email volume or sending behavior is significantly different from yours, it might be safer to advocate for separate IP addresses or distinct shared IP pools.
Clear communication: Establish clear guidelines with partners about sending practices, especially concerning list hygiene and content quality.
IP reputation is still a significant factor for deliverability, especially for internet service providers (ISPs) like Yahoo and Gmail. A strong IP reputation is built on consistent, legitimate sending behavior and avoiding spam complaints. When managing sending for a partner, ensuring that emails originate from a clean, well-maintained IP address is paramount. If you're managing emails for a partner, you must have full visibility into their sending practices to ensure they don't compromise your IP's standing.
The choice between dedicated and shared IPs, and how to manage their reputation, is a critical discussion in any business partnership involving email. You need to consider the volume of emails, the type of emails (transactional vs. marketing), and the partner's historical sending behavior. Maintaining a positive IP reputation with ISPs requires ongoing vigilance.
Authentication protocols and ongoing monitoring
No matter how you structure your domains and IPs, proper email authentication is non-negotiable. This includes SPF, DKIM, and DMARC. These protocols are the foundation of sender trustworthiness and are heavily weighted by ISPs when determining inbox placement.
For domains and subdomains used in a partnership, ensuring these records are correctly configured is critical. Misconfigurations can lead to emails being rejected, flagged as spam, or not even reaching the recipient's server. Each sending domain, including subdomains delegated to an ESP, should have its own set of authenticated records.
Key authentication protocols
SPF (Sender Policy Framework): Authorizes specific IP addresses to send emails on behalf of a domain. It's a critical step in preventing email spoofing and phishing.
DKIM (DomainKeys Identified Mail): Adds a digital signature to outgoing emails, verifying that the email has not been tampered with in transit. Each subdomain requires its own DKIM keys.
DMARC (Domain-based Message Authentication, Reporting & Conformance): Builds upon SPF and DKIM, providing instructions to receiving mail servers on how to handle emails that fail authentication. It also provides valuable reports on email authentication failures. Explore the benefits of DMARC.
Setting up these records correctly for all involved domains and subdomains is the bedrock of good email deliverability in a partnership. It's not enough to set them once, however. Regular monitoring and auditing are essential to ensure continued compliance and optimal performance. For example, Gmail and Yahoo's new sender requirementsemphasize strict authentication and low spam rates.
Ongoing monitoring of both domain and IP reputation is a continuous process. Utilizing tools to track sending metrics, DMARC reports, and blocklist (or blacklist) status is vital. This proactive approach allows you to identify and address any issues quickly before they escalate and significantly impact deliverability for either partner. For instance, you should regularly monitor your domain reputation using Google Postmaster Tools.
Conclusion
Effectively managing email sending domains and IP reputation in business partnerships boils down to clear separation and vigilant oversight. By using distinct subdomains for different types of email traffic and for each partner, you can isolate reputational risks. Coupled with meticulous authentication setup and continuous monitoring, this strategy helps ensure that both parties can maintain high deliverability and protect their brand's email integrity.
Prioritizing transparency and communication regarding email sending practices with your partners will foster a secure and high-performing email ecosystem for everyone involved.
Views from the trenches
Best practices
Always use a subdomain for a partner's email sending, such as email.partnerdomain.com, to isolate reputation.
Delegate the subdomain to your ESP, which is a standard and effective configuration practice.
Implement a gradual warming process for any new sending domains or IP addresses.
Common pitfalls
Using the root domain for bulk or transactional email for a partner, risking the main brand's reputation.
Assuming a partner's sending practices are clean without proper verification or shared monitoring.
Neglecting to warm up new IPs or subdomains, leading to immediate deliverability issues.
Expert tips
Monitor both domain and IP reputation using tools like Google Postmaster to catch issues early.
Establish clear communication channels with partners regarding email sending policies and data hygiene.
Consider shared IPs only for low-volume scenarios with a reputable ESP that actively manages their pools.
Marketer view
A marketer from Email Geeks says that using a subdomain like email.brand.com is the primary reason to protect the root domain from reputation damage. If issues occur with the subdomain, it can be discarded and a new one set up.
2018-09-11 - Email Geeks
Marketer view
A marketer from Email Geeks says that transactional emails should be sent from a separate subdomain and undergo a warming process, similar to a new IP, to establish frequency, volume, and content reputation with ISPs, which mitigates significant risks.
Yahoo and 
Gmail. A strong IP reputation is built on consistent, legitimate sending behavior and avoiding spam complaints. When managing sending for a partner, ensuring that emails originate from a clean, well-maintained IP address is paramount. If you're managing emails for a partner, you must have full visibility into their sending practices to ensure they don't compromise your IP's standing.
