Why are FBLs not available for all domains?

You signed up for a feedback loop (FBL) so you could see who's hitting the spam button. But then you noticed the complaint data barely trickles in, and a huge chunk of your list sits with providers who send nothing back. That's not a bug. It's the normal state of FBLs.

An FBL is a system where a mailbox provider tells you when one of your recipients marks your email as spam. Sounds simple. But running one takes real technical work: the provider has to strip personal data from the complaint, format it into a standard report (usually ARF format), verify the sender's identity, and pipe it out reliably at scale. Not every provider has built that system, and some have chosen not to.

Here's who runs a traditional FBL and who doesn't:

• FBL available: Yahoo Mail, AOL Mail, and most providers running on the same Verizon Media infrastructure. SparkPost (now Bird) also runs an FBL for mail sent through its platform.
• No traditional FBL: Gmail and Outlook. Between them, they cover the majority of inboxes in most English-speaking markets. So if you're only watching FBL data, you're watching a minority of your actual complaints.

Gmail's reasoning is privacy. When a Gmail user hits "Report spam", Gmail uses that signal internally to tune its filters, but it doesn't share which specific user complained. They've made a deliberate choice to keep that data private rather than relay it back to senders. You get aggregate signals through Google Postmaster Tools, but not per-complaint reports.

Outlook's situation is different. Microsoft did run a Junk Mail Reporting Program (JMRP) and Smart Network Data Services (SNDS) for years, but JMRP has been deprecated. What remains is SNDS for IP-level data, not a real-time per-complaint FBL in the traditional sense.

Smaller regional providers often just don't have the engineering resources to build and maintain FBL infrastructure. It's not a priority when they're running lean operations for a relatively small user base.

The practical takeaway is that FBL data alone gives you an incomplete picture of your complaint rate. You need to layer in your ESP's built-in complaint tracking, Google Postmaster Tools for Gmail complaints, and your overall complaint rate trends to understand what's really happening. Treat FBL signals as one data point, not the whole story.

Now if you're unsure whether your FBL is properly configured or want help reading what the data is (or isn't) telling you, our SOS hotline is free. No pitch, just answers.