A domain-wide complaint spike tells you something needs attention. It may not tell you whether the problem came from onboarding, a newsletter or an old-list campaign.

Gmail Feedback Loop can help you group complaint signals around the way your email program is organised.

Ask your ESP what it already sends

Look for a Feedback-ID header in a real message and ask your provider what its fields represent. An ESP may manage the implementation itself. Avoid adding a competing header before understanding the existing one.

The format allows up to three optional identifiers followed by a mandatory sender identifier. For example:

``text Feedback-ID: news-sept:weekly:subscribers:sendpoint ``

This is an illustrative format, not a header to copy into production unchanged. Google's sender identifier must be consistent across the mail stream and contain 5 to 15 characters.

Choose labels that support a decision

Use an identifier for a program you could pause or investigate separately. Keep the meanings distinct across fields so unrelated traffic is not accidentally grouped.

A unique identifier for every message is a poor choice. Google explicitly advises against it. You need enough activity within a group for its signal to be useful.

Complete the technical setup

For a direct implementation, add the header before DKIM signing. Use a signing domain you control and have verified in Postmaster Tools. Google's setup also requires the sending IPs in the signing domain's SPF records and valid PTR records resolving to a hostname.

Ask the provider to verify the complete implementation. Seeing a header in a message does not establish that every requirement has been met.

Read the results as aggregate evidence

The reporting covers gmail.com recipients and depends on sufficient messages and distinct user complaints. It does not give you a list of the individual people who complained. An absent identifier does not prove that nobody complained.

When a group is flagged, compare the actual message, signup source and trigger. If reactivation is the problem, inspect that audience and its expectations. Keep the identifier in your investigation log so the next review follows the same program.

Sources