Which ISPs use DKIM domains for Feedback Loops (FBLs)?
Michael Ko
Co-founder & CEO, Suped
Published 13 Jun 2025
Updated 16 Aug 2025
9 min read
Understanding which Internet Service Providers (ISPs) use DKIM domains for their Feedback Loops (FBLs) is crucial for anyone serious about email deliverability. Feedback loops are a vital mechanism for senders to receive notifications when recipients mark their emails as spam. This information allows senders to promptly remove complainers from their mailing lists, thereby preventing further complaints and protecting their sender reputation.
Historically, FBLs were often tied to sending IP addresses. However, as email authentication evolved, particularly with the widespread adoption of DomainKeys Identified Mail (DKIM), some ISPs began to shift towards domain-based FBLs. This change offers a more granular and often more stable way to identify the source of complaints, as domains are typically more persistent than IP addresses, especially for senders using shared IP pools or multiple sending services.
This guide will explore the major ISPs that utilize DKIM domains for their FBL programs and discuss why understanding these distinctions is important for maintaining a healthy email program. We will also touch upon the broader landscape of FBLs and how to effectively leverage the data they provide.
DKIM (DomainKeys Identified Mail) serves as an email authentication method that uses cryptographic signatures to verify the authenticity of a sender and ensure that the email content has not been tampered with in transit. When an ISP implements a DKIM-based FBL, it means that the spam complaint reports they generate are tied directly to the DKIM domain used to sign the email, rather than just the sending IP address.
This approach enhances accuracy, as the domain acts as a consistent identifier for the brand or entity sending the email. Even if your IP addresses change, as long as your DKIM signing domain remains the same and properly configured, you should continue to receive complaint data. This is particularly beneficial for Email Service Providers (ESPs) who manage sending for multiple clients, as it allows them to tie complaints directly back to the specific client's domain.
To register for a DKIM-based FBL, senders typically need to prove ownership or management of the domain being used for DKIM signing. This often involves setting up specific DNS records or going through a verification process with the ISP or a third-party FBL aggregator. It is a proactive step that demonstrates a sender's commitment to good sending practices and helps ensure they receive timely feedback on recipient complaints.
IP-based FBLs
Identification: Complaints are tied to the specific IP address from which the email originated. This is common for senders with dedicated IPs.
Coverage: Many legacy FBL programs from ISPs like Microsoft (Hotmail/Outlook.com) traditionally operate on an IP-based model.
Limitations: If you change IPs frequently or use shared IPs, tracking complaints effectively can be challenging.
Key ISPs and their FBL types
When it comes to FBLs that explicitly use DKIM domains for their reporting, Yahoo (Oath) stands out as a primary example. Their system is designed to provide feedback based on the DKIM domain used to sign the mail. This includes brands under the Oath umbrella such as AOL and Verizon Mail.
To participate in the Yahoo feedback loop, senders must register their DKIM domains through the Yahoo Senders Hub. This ensures that complaint data is accurately attributed to the correct sending domain, helping you maintain a good sender reputation with Yahoo (Oath) properties.
While Google (Gmail) primarily offers aggregated feedback through Google Postmaster Tools, which relies heavily on DKIM and SPF authentication for data accuracy, it doesn't provide the same per-complaint, DKIM-domain-specific FBL reports as Yahoo. Instead, Google's FBL provides a daily aggregate of complaint rates for authenticated domains and IPs, which is still incredibly valuable but different in its approach.
Other major ISPs, such as Microsoft (Outlook.com), primarily offer IP-based FBLs. While DKIM authentication is crucial for deliverability to these providers, the FBL reports themselves are typically tied to the sending IP. However, companies like Validity, through their FBL aggregation services, can provide a more unified view that integrates both IP and domain-based feedback where available. This allows senders to get a more comprehensive understanding of their complaint data regardless of the specific ISP's FBL implementation.
ISP/Provider
FBL Type
DKIM Domain Usage
Yahoo (Oath)
Domain-based
Directly links complaints to your signed DKIM domain.
Google (Gmail)
Aggregate data (via Postmaster Tools)
Uses DKIM for authentication but provides domain reputation and aggregate complaint rates, not per-complaint data.
Microsoft (Hotmail/Outlook.com)
IP-based
DKIM is essential for authentication, but FBL reports are tied to sending IPs.
Mail.ru (VK Mail)
Primarily IP-based
Offers FBLs that are largely IP-centric. DKIM contributes to overall reputation.
iCloud
None
Does not currently offer a public FBL program.
It is important to understand that while some ISPs do not offer direct DKIM-based FBLs, strong DKIM authentication is still a fundamental requirement for achieving good inbox placement. All major ISPs use DKIM (along with SPF and DMARC) to assess the authenticity and trustworthiness of incoming mail. Therefore, regardless of the FBL mechanism, proper DKIM configuration is non-negotiable for email deliverability.
Benefits and challenges
The primary benefit of utilizing DKIM domains for Feedback Loops is the enhanced ability to tie spam complaints directly to specific domains, offering a clearer picture of your brand's reputation. This is especially useful for senders who manage multiple brands or clients from shared infrastructure, as it allows for precise identification of the source of abuse.
Another significant advantage is the stability of the complaint data. Unlike IP addresses, which can change due to provider shifts or technical configurations, DKIM domains tend to be more static identifiers of a sending entity. This consistency ensures that you continue to receive relevant complaint feedback even if your underlying IP infrastructure changes, providing a more robust mechanism for reputation management.
However, there are challenges. The main limitation is that not all ISPs provide FBLs based on DKIM domains. As seen with Microsoft (Outlook.com), many still rely on IP-based FBLs, meaning senders need to manage both types of feedback streams to get a comprehensive view. This necessitates a multi-faceted approach to FBL data collection and processing, often requiring the use of third-party aggregation services.
Furthermore, proper DKIM configuration is paramount. Any misconfiguration, such as a DKIM body hash mismatch or an incorrectly published record, can prevent FBL data from being accurately delivered or even lead to delivery issues. Senders must regularly monitor their DMARC reports to catch these issues promptly and ensure that both their email authentication and FBL feedback mechanisms are functioning correctly.
Managing FBLs and DKIM alignment
Effective management of FBLs, whether IP or DKIM-based, requires robust systems for processing complaint data. Once you receive an FBL report, the critical next step is to identify the complaining recipient and immediately suppress them from your mailing lists. This not only reduces future complaints but also signals to ISPs that you are a responsible sender, which can positively impact your long-term deliverability.
For email service providers (ESPs), managing DKIM-based FBLs for clients often involves careful DKIM signing practices. Many ESPs use their own signing domains, but for clients who wish to receive DKIM-based FBLs directly, the ESP may need to implement a double DKIM signing strategy or delegate DKIM signing authority. This ensures that the client's domain is the one associated with the FBL, allowing them to directly receive complaint data.
Additionally, senders should monitor not only their FBL data but also their domain and IP reputation. Tools that provide insights into blocklist (or blacklist) status and DMARC reports are essential for a holistic view of email program health. By combining FBL data with other deliverability metrics, you can proactively identify and resolve issues before they significantly impact your inbox placement.
The example above shows a typical DKIM record, which is a TXT record published in your DNS. The `p` tag contains your public key. Proper management of these records is critical for successful DKIM authentication and, by extension, for the functionality of DKIM-based FBLs. Regularly checking your DNS records for accuracy and ensuring that your DKIM keys are properly rotated helps maintain continuous deliverability.
Views from the trenches
Best practices
Always register for all available FBLs, both IP-based and DKIM-based, to maximize complaint data coverage.
Integrate FBL processing into your automated suppression lists to promptly remove complainers.
Regularly monitor your DKIM authentication status using DMARC reports to ensure proper alignment and signing.
For ESPs, clarify with clients how their FBL data will be handled, especially concerning DKIM domain association.
Common pitfalls
Neglecting to register for FBLs, leading to unchecked spam complaints and reputation damage.
Not processing FBL data in a timely manner, resulting in continued mailing to unhappy recipients.
Assuming all FBLs are domain-based or IP-based without verifying with each ISP.
Failing to maintain proper DKIM records, which can invalidate FBL eligibility and impact deliverability.
Expert tips
Leverage FBL data not just for suppression, but for list hygiene and engagement analysis. High complaint rates often indicate poor list quality or irrelevant content.
If using an ESP, understand their FBL collection and reporting methods. Ensure they are transparent about how complaints are handled and attributed.
Consider a DMARC policy of p=quarantine or p=reject for domains that are properly authenticated, as this gives ISPs clearer instructions on handling unauthenticated mail.
Even if an ISP doesn't offer a public FBL, closely monitor your bounce rates and engagement metrics. These can indirectly signal complaint issues.
Marketer view
Marketer from Email Geeks says Google's FBL is more about aggregate data than tracking individual email IDs that reported spam.
2022-07-18 - Email Geeks
Marketer view
Marketer from Email Geeks says Yahoo and AOL are examples of ISPs that allow tracking of specific email IDs that reported spam via their FBLs.
2022-07-18 - Email Geeks
The importance of FBLs for deliverability
While not all ISPs have transitioned to DKIM-based FBLs, their importance is growing. Yahoo (Oath) is a key player in this space, providing domain-specific feedback that is invaluable for senders. Other providers like Google (Gmail) offer aggregate data that heavily relies on DKIM for authentication, even if it's not a direct per-complaint FBL.
For email marketers and deliverability professionals, actively participating in available FBL programs and meticulously processing their data is non-negotiable. It's a fundamental aspect of maintaining a positive sender reputation and ensuring your emails consistently reach the inbox.
Staying informed about which ISPs offer which type of FBL (IP-based, DKIM-based, or aggregate data) is crucial for a comprehensive deliverability strategy. Combined with strong email authentication protocols like SPF, DKIM, and DMARC, leveraging FBL data empowers senders to adapt to recipient feedback and proactively manage their email program's health.
Microsoft (Hotmail/Outlook.com) traditionally operate on an IP-based model.
Yahoo (Oath) stands out as a primary example. Their system is designed to provide feedback based on the DKIM domain used to sign the mail. This includes brands under the Oath umbrella such as AOL and Verizon Mail.
Google (Gmail) primarily offers aggregated feedback through Google Postmaster Tools, which relies heavily on DKIM and SPF authentication for data accuracy, it doesn't provide the same per-complaint, DKIM-domain-specific FBL reports as Yahoo. Instead, Google's FBL provides a daily aggregate of complaint rates for authenticated domains and IPs, which is still incredibly valuable but different in its approach.
Microsoft (Outlook.com), primarily offer IP-based FBLs. While DKIM authentication is crucial for deliverability to these providers, the FBL reports themselves are typically tied to the sending IP. However, companies like Validity, through their FBL aggregation services, can provide a more unified view that integrates both IP and domain-based feedback where available. This allows senders to get a more comprehensive understanding of their complaint data regardless of the specific ISP's FBL implementation.
Google (Gmail)
Mail.ru (VK Mail)
iCloud
