Feedback-ID header generator: see which campaign drives your Gmail spam rate
In short: Builds Feedback-ID: a:b:c:SenderId from up to three identifiers (campaign, customer, mail type) and a SenderId, or reads one you already send, and checks it against Google's rules: SenderId 5-15 characters, colons only as separators, identifiers not repeated across fields, no per-message values such as addresses or UUIDs. Limit: It builds and checks the header; it can't add it to your mail or confirm Postmaster Tools is reporting on it.
Fill in up to three identifiers (for example campaign, customer and mail type) and a SenderId of 5 to 15 characters that stays the same on all your mail. The tool writes the Feedback-ID: a:b:c:SenderId header and checks it against Google's rules, so Postmaster Tools' Feedback Loop can show a spam rate per campaign.
Price: this tool is free. Checking a whole email list is from $9/mo, and the first 100 checks are free with Google, no card. See pricing
Build the header
Or check a header you already send
Built in your browser. Nothing is sent anywhere.
Sample result
Feedback-ID: oct-sale:newsletter:promo:northwind1 follows Google's format.
- SenderId
- northwind1
- Identifiers
- 3
- Length
- 10 of 5-15
What this means for you
Add it to DKIM-signed mail and Postmaster Tools can show a spam rate per campaign.
- Builds a:b:c:SenderId
- Reads a header you already send
- Flags per-message values
- Flags repeated identifiers
- Feedback-ID
- Postmaster Tools
- Gmail
By SimpleVerifier Team · Last updated · Runs in your browser; nothing you paste is sent to us
How do I keep the campaign that spikes from bouncing too?
- Once Postmaster shows which identifier drew the reports, pause that campaign's list.
- Upload the list at /verify to remove dead and disposable addresses. The first 100 email checks are free with a Google sign-in, no card.
- Send it again only to people who asked for it.
How do I add a Feedback-ID header?
- Decide what you want spam rates split by: usually campaign, then customer or brand, then mail type.
- Enter those as identifiers a, b and c, and a SenderId that is the same on every message of the stream.
- Fix anything the checks flag, then copy the header.
- Add it as a custom header in your sending platform or mail server, on DKIM-signed mail from a domain verified in Postmaster Tools.
Example
- You enter
- Identifiers
oct-sale,newsletterandpromo, and the SenderIdnorthwind1. - You get
Feedback-ID: oct-sale:newsletter:promo:northwind1, with no problems flagged: a 10-character SenderId, no colons inside fields and no identifier repeated or unique per message.- Limits
- Runs in your browser.
What Google's Feedback Loop needs
Google's Feedback Loop help defines the header as Feedback-ID: a:b:c:SenderId: up to three optional identifiers chosen by the sender for campaign, customer or other use, then a mandatory SenderId of 5 to 15 characters that should be consistent across the mail stream. Data is generated for the first four colon-separated fields counted from the right, and none at all when SenderId is empty.
Each identifier is aggregated on its own, so Google asks that identifiers aren't repeated across fields, and that none is unique to every message: a recipient address, a UUID or a message ID never reaches the volume needed for a report. Reports appear only for identifiers with enough volume and spam reports on a given day, and cover only @gmail.com recipients.
Before it shows up in Postmaster Tools
The mail must be DKIM-signed by a domain you own and have verified in Postmaster Tools, the sending IPs must be in that domain's SPF record and have PTR records, and each stream should carry only one Feedback-ID. Some platforms already set one: Amazon SES adds its own and lets you add two identifiers through the ses:feedback-id-a and ses:feedback-id-b message tags.
With it in place, a spike in Postmaster Tools can be traced to one campaign instead of the whole domain. Track the daily rate afterwards with the Postmaster spam rate tracker.
Who uses this tool, and for what?
- ESP and SaaS developers
- Tag each customer's mail so one customer's spam spike shows up as theirs.
- Email marketers
- Split Gmail spam rate by campaign instead of guessing which send caused it.
- Self-hosted senders
- Check a header already in production against Google's rules.
What can’t this tool tell you?
- It builds and checks the header; it can't add it to your mail or confirm Postmaster Tools is reporting on it.
- Gmail reports only identifiers with enough volume and spam reports, and only for @gmail.com recipients.
- The character advice (plain ASCII, no spaces) is the safe choice for a header value, not a rule Google publishes.
Common questions
- What should the SenderId be?
- A stable 5-15 character identifier of your own, such as your brand or stream name. It must stay the same across the mail stream.
- Can I put the recipient's email in Feedback-ID?
- No. Google says not to use a value that is unique to every message; it would never reach the volume needed for a report.
- Do I need all three identifiers?
- No, they're optional. With only a SenderId you get one rate for the whole stream; adding a campaign identifier shows which campaign drew the reports.
- Is anything sent anywhere?
- No. The header is built in your browser.
Sources
Authentication and capacity are half of deliverability.
The other half is who you send to. Every hard bounce counts against the domain and inboxes you are sending from, and nothing in DNS can tell you which addresses on your list are dead.
- Bulk verification with real SMTP mailbox checks
- Hard bounces removed before a send, not discovered after
- Catch-all, disposable and role detection on every row
Plans from $9 a month, cancel anytime, no contract. Sign in with Google and your first 100 email checks are free, no card. The free tools stay free either way.