Understanding Feedback Loops
What is an email feedback loop?
An email feedback loop, also known as a complaint feedback loop, enables an Internet service provider (ISP) to inform a sending organization about spam complaints submitted by recipients of their messages. Doing so enables the sender to remove those email subscribers from their lists and ensure they won’t continue to receive unwanted messages and file more spam complaints.
Removing email subscribers who have filed complaints also helps keep a sending organization’s spam complaint rate low. The lower a sender’s spam complaint rate is, the better their chances of successfully reaching recipients’ inboxes in the future, because ISPs won’t be as likely to quarantine or reject their messages.
How does an email feedback loop work?
Each ISP offers its own feedback loop (FBL), and it’s incumbent on a sending organization, whether that’s an email service provider (ESP) like Bird or a business handling email on its own, to register for each one. A typical FBL uses a button or a link to a form that allows a recipient to register a complaint about unwanted email.
Some ISPs send the details of each individual spam complaint to the sending organization while others, such as Gmail, provide aggregate data that doesn’t say which recipients filed complaints.
| Protocol | What it provides | Notes |
|---|---|---|
| Individual FBL | Sends each spam complaint with recipient-level detail | Helpful for precise list hygiene |
| Aggregate FBL | Sends summary-level complaint data only | Used by Gmail and some major ISPs |
The business that generated the email should immediately remove people who file spam complaints from their mailing list, preferably through an automated process that eliminates the potential for human error.
Why should you care about an FBL?
Maintain a suppression list (or exclusion list) for addresses that file spam complaints or produce a hard bounce, and honor unsubscribe requests promptly. (A soft bounce means there was a temporary error or delay, so the address can be tried again.)
If you repeatedly send email to people who should be suppressed or who have opted out, your sending reputation will take a hit. ISPs will limit delivery of email from you to inboxes on their network, and will refuse all messages from you if your sending reputation drops too low.
How does Bird work with FBLs?
Bird registers with major ISPs’ feedback loops and manages suppression lists and unsubscribe links automatically:
- Spam complaints (FBLs) and hard bounces: When a mailbox provider reports a spam complaint through an FBL or returns a hard bounce, Bird automatically adds that recipient address to your workspace suppression list so future sends to that address are blocked.
- Unsubscribe requests: When a recipient clicks an unsubscribe link or uses the one-click
List-Unsubscribeheader on a marketing message, Bird updates their recipient subscription preferences so they no longer receive marketing broadcasts while still allowing critical transactional messages. - API and dashboard management: You can inspect, add, or remove entries in your workspace suppression list through the Bird API or dashboard.
Learn More about FBLs
Dig deeper into useful FBL resources
Here are some resources that will help you dig deeper into FBLs:
- Wikipedia’s entry on email FBLs: This is a good overview of how FBLs work.
- A list of IP-based, aggregated, and domain-based FBLs: This list is maintained by the Messaging, Malware and Mobile Anti-Abuse Working Group.