What is “Feedback-ID”?

Feedback-ID is a header used primarily with Gmail's Feedback Loop. It provides identifiers that Gmail includes in aggregate spam complaint reports, helping senders identify which campaigns or customer accounts generate complaints.

Format: Feedback-ID: campaign-123:customer-456:mailtype-marketing:sender-789

The header contains up to four colon-separated identifiers. ESPs typically use:

Campaign or message identifier

Customer or account identifier

Mail type (transactional, marketing, etc.)

Sender or list identifier

Gmail aggregates complaint data by these identifiers and reports it through Postmaster Tools. Instead of seeing "you had 100 complaints," you can see "campaign X had 80 complaints, campaign Y had 20."

This granularity is valuable for:

Identifying problematic campaigns quickly

Tracking complaint rates per customer on shared infrastructure

Segmenting feedback data for analysis

ESPs configure Feedback-ID automatically. If you're building your own sending system, add this header with meaningful identifiers to enable granular feedback analysis.

It's the cargo manifest number. When complaints arrive, you know exactly which shipment caused the problem.