Setting Up a Gmail Feedback-ID Header So Postmaster Tools Shows Spam Rate per Campaign

Add one header to your marketing mail, Feedback-ID: campaign:customer:type:SenderId, with a SenderId of 5 to 15 characters that never changes, on mail DKIM-signed by a domain verified in Postmaster Tools. When a campaign draws enough spam reports, Postmaster's Feedback Loop dashboard shows its spam rate on its own instead of hiding it in the domain's average.

The Feedback-ID header generator builds the header and checks one you already send against Google's rules. Sources, read 2 November 2026: Google's Feedback Loop help and the Amazon SES sending review FAQ (Feedback-ID note).

Google's rules

Rule	Detail
Format	Feedback-ID: a:b:c:SenderId
a, b, c	Optional; up to three identifiers for campaign, customer or other grouping
SenderId	Mandatory, 5–15 characters, consistent across the stream; empty means no data
No repeats	Don't use the same value in two fields on a day's traffic
Nothing per-message	No addresses, UUIDs or message IDs
One header	Only one Feedback-ID per message
Authentication	DKIM-signed by a domain you own, applied after the header is added; domain verified in Postmaster Tools
IPs	In the signing domain's SPF record, with PTR records resolving to a valid hostname
Coverage	@gmail.com recipients only
Threshold	Only identifiers with enough volume and distinct spam reports that day

Choosing the fields

1. Decide what you want split. Usually campaign first, then customer or brand, then mail type (newsletter, promo, onboarding).
2. Keep each identifier at a volume that can report. A campaign that goes to 500 Gmail users a day won't reach Google's threshold; group small sends by type instead.
3. Make the SenderId your stream. acmenews for the newsletter, acmepromo for promotions. It must stay the same on every message in that stream.
4. Use plain ASCII, no spaces, no colons inside a field. Colons are the separators. (No spaces is the safe choice, not a rule Google states.)
5. Example: Feedback-ID: oct-sale:acme:promo:acmepromo.

Adding it

Most ESPs and sending APIs allow custom headers on a campaign or per message. Add it before DKIM signing happens, which with an ESP is automatic. If you send through Amazon SES, SES already sets a Feedback-ID of its own; add your identifiers with the ses:feedback-id-a and ses:feedback-id-b message tags rather than a second header.

Using it after a spike

When Postmaster's spam rate jumps, the Feedback Loop dashboard lists identifiers with unusual spam rates. That turns "the domain spiked" into "the October sale to the reactivated segment spiked", which is what you need to stop mailing. Then follow the daily rate as in counting the 7 days below 0.3%. For the dashboards themselves, see reading Google Postmaster Tools; for per-message reports from other providers, reading feedback loop reports.

Limits

The header only helps for Gmail recipients and only once an identifier gets enough reports to show. It doesn't lower the spam rate; it tells you where it came from.

Where SimpleVerifier fits

Once you know which campaign's list drew the reports, pause it and upload it at /verify to remove dead and disposable addresses before it's mailed again, with permission. The first 100 checks are free with a Google sign-in. Pro is $39 a month with the first 100,000 checks a month at full speed, then slower, never cut off. See pricing.