How to setup Yahoo FBL with Sendinblue dedicated IP and Microsoft Office 365?
Matthew Whittaker
Co-founder & CTO, Suped
Published 15 Jul 2025
Updated 16 Aug 2025
10 min read
Navigating the complexities of email deliverability often involves intricate setups, especially when dealing with multiple service providers. One such challenge arises when trying to set up a Yahoo Feedback Loop (FBL) for a domain that uses a dedicated IP address with an Email Service Provider (ESP) like Sendinblue, while its primary email hosting is handled by Microsoft Office 365. I have seen this scenario many times, and it requires a clear understanding of how these systems interact.
The core issue typically revolves around where Yahoo sends the FBL verification email. Yahoo, being a major Mailbox Provider, requires verification of domain ownership to ensure that FBL data is only provided to legitimate senders. This verification usually involves sending an email to a designated abuse or postmaster address for the domain or subdomain that is DKIM-signing the emails.
When your primary domain’s MX records point to Office 365, but your sub-domain, used for bulk sending, is authenticated by Sendinblue, it creates a split in email handling. This setup can lead to a situation where the FBL verification email, intended for the sending sub-domain, attempts to go to an address that Office 365 doesn't manage, causing a roadblock in the FBL setup process. Understanding how Yahoo's Sender Hub operates is key to resolving these challenges.
Understanding Yahoo FBL and DKIM
A Feedback Loop (FBL), also sometimes referred to as a Complaint Feedback Loop (CFL) or a blocklist, is a system that allows Internet Service Providers (ISPs) to report user complaints (e.g., when a recipient clicks the "This is spam" button) back to the sender. This data is crucial for maintaining a good sender reputation and avoiding email blacklists (or blocklists). Yahoo's FBL is an essential tool for anyone sending email to Yahoo Mail users.
When you apply for the Yahoo FBL, they require proof of ownership for the domain that is DKIM-signing your emails. If you are using a dedicated IP through Sendinblue, Sendinblue will likely be signing your emails with two DKIM signatures: one for your sending sub-domain (e.g., foo.example.com) and another for their own internal domain (e.g., sendib.com). Yahoo will specifically look for the domain that aligns with the d= tag in your DKIM signature when sending the FBL verification email. If your sending sub-domain is foo.example.com, the verification will be sent to postmaster@foo.example.com.
The Yahoo FBL reports provide insight into spam complaints, which is critical for maintaining a healthy sending reputation. You can also monitor your sending reputation and performance through Yahoo's deliverability performance feeds, which offer data beyond just FBL complaints. This is similar to how Google Postmaster Tools provides insights for Gmail. You can learn more about Yahoo FBL setup in our dedicated guide on what a Yahoo FBL is and how to set one up.
The multi-provider challenge
The primary challenge in this scenario is managing the email flow for the specific postmaster address. If your main domain (example.com) is hosted on Microsoft Office 365, all mail for that domain, including sub-domains (unless explicitly configured otherwise), will be routed through Office 365's MX records. This means that postmaster@foo.example.com would attempt to be delivered to your Office 365 environment, even if foo.example.com is primarily used with Sendinblue.
Many ESPs, including Sendinblue (now Brevo), handle FBL registrations for their shared and dedicated IP pools. They often use a technique called "double DKIM signing." This means that in addition to your domain's DKIM signature, their own domain's DKIM signature is also added to the email headers. This allows them to receive FBL data directly because their domain is already registered for FBLs, streamlining the process for their customers.
Before proceeding with any manual setup, it's crucial to confirm with Sendinblue if they already handle the Yahoo FBL for your dedicated IP and the associated sending domain. Most reputable ESPs will have this covered to ensure good deliverability for their users.
Scenario: Split email handling
Sending Domain: Your sub-domain (e.g., foo.example.com) authenticates with Sendinblue and its dedicated IP.
Main Domain Email: Your root domain (e.g., example.com) receives all its email via Microsoft Office 365.
FBL Verification: Yahoo sends the verification email to postmaster@foo.example.com.
Impact and solution direction
Email Routing: Office 365 will try to deliver the postmaster email.
ESP Role:Sendinblue (Brevo) often handles FBLs directly via double DKIM signing, making separate registration unnecessary.
Solution: Verify FBL management with Sendinblue first. If not covered, explore options to create a mailbox or redirect for postmaster@foo.example.com within Office 365, or a forwarding rule. This is how you access Yahoo FBL.
Strategies for FBL setup and troubleshooting
The primary course of action is always to first reach out to your ESP, Sendinblue in this case. In many instances, they already have agreements and systems in place to manage FBLs on behalf of their users. Their use of double DKIM signing is a common practice specifically for this purpose. If they confirm they manage the Yahoo FBL for your dedicated IP and sending domain, then no further action is required on your part for Yahoo FBL setup. This can prevent unnecessary manual configuration and potential issues.
If, however, Sendinblue does not manage the Yahoo FBL for your specific setup, or if you prefer to have direct access, you will need to ensure that the postmaster@foo.example.com email address can receive mail. Given that your main domain (example.com) is hosted on Office 365, mail for foo.example.com will likely be routed there. You would then need to create a mailbox for postmaster@foo.example.com within your Office 365 environment, or set up a forwarding rule from this address to an active mailbox you monitor. This approach ensures you receive the Yahoo FBL verification email and subsequent reports. For more details on troubleshooting, you can refer to our guide on contacting Yahoo's postmaster team.
Here's an example of how you might create a DNS record if your sub-domain's mail flow needed specific routing to ensure the postmaster email is received:
Example MX Record for Sub-domainDNS
foo.example.com. IN MX 10 mail.foo.example.com.
Another option for Yahoo FBL setup, especially if the postmaster@ address is problematic, is to explore alternative verification methods if Yahoo offers them, or to use an email alias. If Office 365 is your primary mail provider, setting up a mail user or contact in Outlook that forwards to an accessible inbox might be the simplest solution. This allows Yahoo's verification email to reach you, even if a direct mailbox for that specific sub-domain is not intended.
It's worth noting that if your ESP (Sendinblue) is already double-signing your emails with their own domain, they are likely receiving the FBL data for the messages sent through their platform. In such cases, requesting the data from them directly might be more efficient than trying to set up a separate FBL. They can provide aggregated complaint data, helping you to understand your email performance and prevent your dedicated IP from ending up on a blacklist or blocklist.
Remember that Yahoo (now part of Verizon Media) offers a Sender Hub, which is their equivalent of a postmaster tool. While it may not provide as granular data as Google Postmaster Tools or Microsoft SNDS, it is still beneficial for monitoring your sending to Yahoo properties. Always try to register your sending domains and IPs with available postmaster tools for better visibility into your reputation.
Beyond FBLs: Holistic deliverability management
Setting up FBLs is just one piece of the deliverability puzzle. To ensure consistent inbox placement and maintain a healthy sender reputation, a holistic approach is necessary. This involves consistently monitoring your email performance, adhering to best practices, and actively managing your sending infrastructure.
Regularly check your sender score and monitor for any signs of being added to a blocklist (or blacklist). Tools like blocklist monitoring can alert you quickly if your dedicated IP or domain is listed. Also, pay close attention to your DMARC reports, as these provide valuable feedback on authentication failures and potential abuse, helping you prevent your emails from going to spam. Our DMARC monitoring service can assist with this. Addressing issues such as high bounce rates with Yahoo is also important for deliverability.
Ensure your SPF and DKIM records are correctly configured for both your main domain and any sub-domains used for sending. Even with a dedicated IP, proper authentication is non-negotiable for email deliverability. Misconfigurations, such as SPF DNS timeouts, can lead to deliverability issues, particularly with Microsoft. Learn more about why emails fail at Microsoft due to hidden SPF DNS timeouts.
Finally, maintaining a clean and engaged email list is paramount. High complaint rates, often reported through FBLs, are a strong indicator of poor list hygiene or irrelevant content, which can quickly lead to your dedicated IP being blacklisted. Combine FBL data with other postmaster tools to get a comprehensive view of your email program's health and take corrective actions promptly.
Views from the trenches
Best practices
Always consult with your ESP (e.g., Sendinblue) first to confirm their FBL management policies for dedicated IPs.
Utilize sub-domains for sending bulk or marketing emails to isolate their reputation from your main domain's reputation.
Set up email forwarding for postmaster or abuse addresses if direct mailbox creation isn't feasible with your primary mail host.
Actively monitor all available postmaster tools, including Yahoo, Google, and Microsoft, to stay informed about your reputation.
Common pitfalls
Assuming your ESP automatically manages all FBLs without explicit confirmation or understanding their method (e.g., double DKIM signing).
Not creating a functional postmaster mailbox or forwarding rule for the DKIM-signing domain when required for FBL verification.
Overlooking the importance of segmenting email traffic by using dedicated IPs and sub-domains, leading to broad impact on reputation.
Failing to regularly check blacklists (or blocklists) and address any listings promptly, which can severely impact deliverability.
Expert tips
Leverage DMARC reports to identify authentication issues, which can indirectly affect your FBL effectiveness and overall deliverability.
Implement a consistent IP warming strategy for new dedicated IPs to build a positive sending reputation gradually.
Regularly clean your email lists to remove inactive or invalid addresses, reducing bounces and complaint rates.
Ensure your email content is relevant and engaging to minimize spam complaints, a direct input to FBLs.
Expert view
Expert from Email Geeks says many ESPs leverage double signing to gain easier access to their FBLs, simplifying the process for clients.
2021-06-16 - Email Geeks
Marketer view
Marketer from Email Geeks says that if an ESP handles Yahoo FBL as a default with double signing, everything should be good.
2021-06-17 - Email Geeks
Key takeaways for Yahoo FBL and beyond
Setting up the Yahoo FBL with a Sendinblue dedicated IP and Microsoft Office 365 involves understanding the interplay between DKIM signing and mail routing. The most efficient first step is to confirm with Sendinblue (Brevo) whether they already manage the Yahoo FBL for your dedicated IP and sending domain through their double DKIM signing process. This is often the case and simplifies the entire setup.
If manual setup is required, ensuring that postmaster@foo.example.com can receive mail through your Office 365 environment, whether via a direct mailbox or a forwarding rule, is critical. Beyond FBLs, always prioritize comprehensive deliverability management, including DMARC monitoring, proactive blacklist (or blocklist) checks, and adherence to email best practices. This multi-faceted approach ensures optimal inbox placement and maintains a strong sender reputation across all mailbox providers.
Microsoft Office 365. I have seen this scenario many times, and it requires a clear understanding of how these systems interact.
Yahoo Mail users.
Google Postmaster Tools provides insights for Gmail. You can learn more about Yahoo FBL setup in our dedicated guide on what a Yahoo FBL is and how to set one up.
Microsoft Office 365.
Sendinblue (Brevo) often handles FBLs directly via double DKIM signing, making separate registration unnecessary.
Outlook that forwards to an accessible inbox might be the simplest solution. This allows Yahoo's verification email to reach you, even if a direct mailbox for that specific sub-domain is not intended.
Google Postmaster Tools or 
