Do B2B mail providers prioritize IP or domain reputation, or both?
Michael Ko
Co-founder & CEO, Suped
Published 6 Aug 2025
Updated 18 Aug 2025
6 min read
For many B2B senders, email deliverability can feel like a complex puzzle. One of the most common questions revolves around how mailbox providers (MBPs) and anti-spam filters actually evaluate incoming mail. Is it primarily about the sending IP address, the domain name, or is it a more nuanced combination of both?
The short answer is that B2B mail providers prioritize both IP and domain reputation, but the weight given to each has evolved over time. While IP reputation remains important, domain reputation has significantly grown in prominence and is often considered the primary factor for many large inbox providers, especially for business-to-business communications.
The evolving landscape of email reputation
Historically, IP reputation was the dominant factor in email deliverability. Internet service providers (ISPs) would largely determine whether an email was legitimate or spam based on the sender's IP address history. A clean IP meant your emails had a good chance of landing in the inbox.
However, with the rise of cloud-based email services, shared IP pools, and sophisticated spamming techniques, relying solely on IP reputation became insufficient. Many legitimate senders use shared IP addresses, meaning their reputation could be unfairly impacted by other senders using the same IP. This led to a shift in focus towards domain reputation, which provides a more granular and brand-specific assessment of sender trustworthiness.
Today, it's about a holistic sender reputation. This encompasses both the IP address and the sending domain, alongside other crucial factors like content quality, engagement, and authentication. For a deeper dive into these concepts, you can explore the difference between IP and domain reputation.
How IP reputation works for B2B
IP reputation is tied to the numerical address from which your emails originate. A high IP reputation indicates that the IP address has a history of sending legitimate, wanted emails, while a low reputation suggests a history of spam or unwanted mail.
For B2B mail, IP reputation plays a foundational role. Even with strong domain reputation, a blacklisted IP address (also known as a blocklisted IP address) will severely hinder deliverability. Many corporate firewalls and spam filters still rely heavily on IP blocklists (or blacklists) to filter out known bad senders. Regularly checking your blocklist status is a critical step in maintaining good email hygiene.
The type of IP you use, shared or dedicated, also impacts how its reputation is managed. Dedicated IPs offer more control but require diligent warming and maintenance. Shared IPs rely on the collective sending behavior of all users, which can be a double-edged sword.
Shared IP addresses
Pros: Often come pre-warmed, easier for low-volume senders.
Cons: Reputation can be affected by other senders' poor practices.
Maintenance: Consistent monitoring and adherence to best practices are key. Maintaining dedicated IP reputation with ISPs is an ongoing effort.
The significance of domain reputation
Domain reputation is a score assigned to your sending domain. This score reflects the overall trustworthiness and health of your email program, separate from the specific IP address used. It's built over time based on various signals, and B2B providers are increasingly leveraging it.
Key factors influencing domain reputation include subscriber engagement (opens, clicks, replies), spam complaints, bounce rates, and whether your emails pass authentication checks like SPF, DKIM, and DMARC. A strong domain reputation signals to MBPs that emails from your brand are generally wanted by recipients. Mailbox providers such as Gmail and Yahoo prioritize domain-based filtering more than IP reputation alone.
For B2B communications, where brand identity and trust are paramount, domain reputation often carries more weight. It's a more persistent identifier than an IP address, especially when considering shared IP pools. Maintaining a positive domain reputation involves consistent monitoring and adherence to deliverability best practices. Understanding how domain reputation is measured is crucial for B2B success.
Best practices for domain reputation
Authenticate: Implement SPF, DKIM, and DMARC. These authenticate your sending domain.
Content quality: Send relevant and engaging content to reduce spam complaints.
List hygiene: Regularly clean your email lists to remove inactive or invalid addresses.
Monitor feedback loops: Pay attention to spam complaints and adjust sending practices accordingly.
Subdomains: Use separate subdomains for different sending purposes (e.g., marketing, transactional) to isolate reputation risks. Read more about managing subdomain reputation.
The interplay and provider specific nuances
While domain reputation is increasingly central, B2B mail providers do not completely disregard IP reputation. Instead, they use a sophisticated combination of both. Some providers may weigh one more heavily than the other, but the overall sender reputation is a blend of these elements.
For instance, Microsoft often places a strong emphasis on IP reputation while Gmail has famously shifted its focus towards domain reputation. Yahoo (AOL/Verizon Media) tends to split the difference, looking at both factors significantly.
The key takeaway is that both IP and domain reputation contribute to your overall sender score. A negative signal from one can impact the other, and a strong performance in both areas ensures the best possible deliverability. It's not an either/or scenario but a complementary one, where a robust strategy addresses both aspects of your email sending infrastructure. B2B senders with low engagement must pay close attention to both.
Mailbox provider
IP reputation focus
Domain reputation focus
Gmail
Moderate, especially for new IPs or bulk senders
High, particularly user engagement metrics
Outlook
High, including SmartScreen filtering
Moderate, also considers DMARC alignment and content.
Yahoo
Significant, especially for identifying unwanted mail.
Significant, balancing with IP reputation for holistic view.
Views from the trenches
Best practices
Maintain strong email authentication (SPF, DKIM, DMARC) for both your domain and any subdomains.
Regularly monitor your IP and domain reputation using tools like Google Postmaster Tools.
Segment your email lists and tailor content to ensure high engagement and low complaint rates.
Implement a consistent sending volume and schedule, avoiding sudden spikes.
Remove invalid or inactive addresses from your lists to prevent bounces and spam trap hits.
Common pitfalls
Ignoring spam complaints or low engagement metrics from your email campaigns.
Not warming up new dedicated IP addresses or subdomains sufficiently.
Sending emails to purchased or old lists, which can contain spam traps.
Failing to monitor blocklists (or blacklists) for both your IP and domain.
Using generic 'From' addresses or lacking proper branding in email headers.
Expert tips
Always prioritize recipient engagement. If your emails are consistently opened and clicked, both your IP and domain reputation will benefit.
Even if you use a shared IP, your domain reputation is still crucial. Focus on your sending practices.
Understand that different B2B mailbox providers have varying weighting preferences. A universal good sending practice is key.
A spike in bounces can severely damage both IP and domain reputation, so list cleaning is paramount.
Consider transactional emails separately from marketing emails using different subdomains and IPs to protect your core domain's reputation.
Expert view
Expert from Email Geeks says mailbox providers evaluate both IP and domain reputation, along with organization-level blocks based on recipient complaints. They also use trap networks, often with recycled client addresses, to identify poor data practices.
2025-05-16 - Email Geeks
Expert view
Expert from Email Geeks says Microsoft and Google are significant providers of filtering services to businesses and use more sophisticated algorithms for email evaluation.
2025-05-16 - Email Geeks
A balanced approach to B2B deliverability
Ultimately, B2B mail providers consider both IP and domain reputation when determining inbox placement. While the emphasis has gradually shifted towards domain reputation as the primary indicator of a sender's trustworthiness, IP reputation still serves as a fundamental layer of defense against spam and abuse.
For successful B2B email deliverability, you need to cultivate a positive reputation for both your IP address(es) and your sending domain(s). This involves adhering to email authentication standards, sending high-quality, engaging content to a clean list, and consistently monitoring your performance metrics. Ignoring either factor can lead to your emails being filtered into spam folders, or worse, completely blocklisted (or blacklisted).
often places a strong emphasis on IP reputation while Gmail has famously shifted its focus towards domain reputation. Yahoo (AOL/Verizon Media) tends to split the difference, looking at both factors significantly.
Gmail
Outlook
Yahoo
