Unlike a number of mailbox providers that offer a standard complaint feedback loop, Google offers the ability for senders to have access to a series of dashboards that display metrics about mail sent to Google users. This access is granted through a service that Google calls Postmaster Tools, and in this article I’ll explain a bit about how to get access to this data. Note that you yourself must have a Google or Gmail account in order to take advantage of this service.


The first step to getting access to this data is to register an authentication domain. An authentication domain is either a domain you use to DKIM sign your mail or your bounce (a.k.a., Return-Path) domain if you publish an SPF record. Registration is simple; enter the domain name on Google’s Postmaster Tools website, create a DNS record specified by Google to prove that you own the domain, validate your DNS record, and you’re done. If you’re a SparkPost Enterprise or SparkPost Premium customer and you’ve delegated DNS ownership of your authentication domain to us, then we will register your domain for viewing by our Deliverability Support team. In such cases, we can share access to your domain’s data with you if you’d like, or if you’re an Enterprise or Premium customer managing your own DNS, you can share your data with us.

Available Data

The following tabs are available in the Google Postmaster Tools dashboard:

  • Spam Rate – What percentage of your DKIM-authenticated mail caused Gmail users to complain
  • Domain and IP Reputation – What Google thinks of your domain(s) and the IP(s) from which they’ve seen your authenticated mail
  • Authentication – How much traffic using your authentication domain(s) has passed authentication checks – SPF, DKIM, and/or DMARC, as applicable
  • Encryption – How much of your mail was sent using TLS encryption between the sending server and Google’s servers.
  • Delivery Errors – Various metrics showing errors that your authenticated mail may have experienced.
    Feedback Loop – See below

The only requirement to see the data on these tabs, other than the Feedback Loop tab, is to just send mail to Google in sufficient volume; Google doesn’t explicitly say how much, instead using the phrase “a sizable daily volume of email traffic (up to the order of hundreds)”.

Feedback Loop

Google’s Feedback Loop does not function like a traditional one; there is no FBL address for you to enter, and you do not get copies of messages that generated complaints. Instead, if you insert a carefully crafted header into your outbound mail, you can track FBL data in your dashboard across up to four different categories.

The Feedback-ID Header

The key to getting FBL data from Google is to add a Feedback-ID header to each of your messages; the format for this header is as follows:

Feedback-ID: a:b:c:SenderId

The SenderId field is a mandatory unique identifier (5-15 characters long) chosen by you, the sender, and it must be the same for all mail sent on a given mail stream.

The other three fields are optional, and can be embedded to track FBL data at the campaign, customer, or other level, such as in this example:

Feedback-ID: CampaignIDX:CustomerID2:MailTypeID3:SenderId

Aggregate data is generated for each of up to four identifiers in the header, starting from the right-most identifier (the SenderId identifier) and displayed on the Feedback Loop tab of the Postmaster Tools dashboard.


This document isn’t meant to be an exhaustive reference to Google’s Postmaster Tools; Google obviously does a much better job on their website of explaining things in more detail. However, we at SparkPost feel like we have a good understanding of how to enroll and how to get value out of your enrollment, so we stand willing to assist our customers in any way that’s needed.