What are Spam Complaints & How to Reduce Them


For 2022, Webbula is launching a series of blog posts about email deliverability topics. We have a variety of esteemed authors from the email industry lined up to participate. 

Previous Articles in the Deliverability Series
  • Subscriber Management: How to Start, Maintain, and Break Up by Elizabeth Jacobi. Read it.
  • Email Opt-Ins: It's All About Consent In the End by Matthew Vernhout. Read it here.
  • Email Authentication 101: What It Is And Why It Is Important For Brand Reputation by Yanna-Torry Aspraki. Read it here.
  • Why Blocklists Make Us Better Email Marketers by Andrew Kordek. Read it
  • IP Warming - Do It Right or Do It Twice by Amanda Jackson. Read it
    Email Deliverability and Subject Lines by Dela Quist. Read it
  • Email List Cleaning: 6 Tips For Mastering a Clean, Active Email List to Achieve High Deliverability by Jack Wrigley. Read it
  • Embrace Your Email Unsubscribe: 6 Recommendations to Optimize Your Unsubscribe Process for the Holiday Season By Mathias Ullrich. Read it
  • 9 Examples of Email Bounces and How to Analyze Them By LoriBeth Blair Read it
  • What are spam traps and can you actually avoid them. By Melissa Lambert. Read it
  • What Does Content Have to Do with Email Deliverability? By Sella Yoffe. Read it. 

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What is a Spam Complaint?

A spam complaint is a report generated by the recipient or mailbox provider as a result of an unwanted email in their Inbox and sent back to the responsible party once someone clicks on the “Report as Spam” button. This only includes recipients clicking on the button and not recipients who receive your emails in the spam or junk folder.

The reports can be: 

  •  manual, written by a person to the sender or to the relaying party in a competent way.

In most cases, the most obvious way is to forward an email to the abuse@ mailbox for the party responsible for the message delivery. The contact information can be taken from the email header source/whois information for relaying IP or a hoster.

The email forward will have all the required technical information for the sender side to analyze the abuse complaint and ensure they remove the complainer from their mailing list.

  •  automated, via Feedback loop. 

Those reports are generated from specific inboxes when your emails are being reported as spam within the mailbox provider interface or an email client.

If your mailbox provider supports a spam reporting button, which is an easier way to complain about a message with one click within an email application (web browser) and mark your email as spam/junk, within most email applications. In such case, the automated Feedback report will be generated and sent back to the sender.


What is a Feedback loop report?


A feedback loop (FBL), is a form of feedback by which a mailbox provider forwards the complaints originating from their users to the sender's organizations. 

The Abuse Reporting Format (ARF) is the standard format for Feedback reports. In most cases, an abuse report consists of a human-readable part, followed by a machine-readable part, and finally the original message. Some report formats might differ, for example, Microsoft uses its own format for such reports, but the overall idea is the same.

Below is an example of an ARF complaint sent by Ziggo.nl

The attachment itself has the following data, which you can use to track the recipient who made the complaint.

What is the acceptable spam complaint rate?


The acceptable spam complaint rate varies between mailbox providers which also depends on the time frame for how long the complaints were consistently high or low, spikes, etc.

It is good to alert the sender if his complaint rate starts to grow to more than 0.2% within the FBL provider. In case a sender is implementing best practices and correct list management then their complaint rate shall always be lower than 0.1%. 


How to set up/apply for the Feedback loop report?


In the first place you need to create/collect the following data: 

  • Feedback loop email address which you will be using to receive the reports;

Feedback loop email addresses can be different, such as fbl@"yourdomain".

  • List of sending IP addresses with the appropriate setup;

As an example, the FAQ SNDS description has been taken (https://sendersupport.olc.protection.outlook.com/snds/FAQ.aspx)

In order to validate the authority to receive the data for the IPs you need to have the appropriate contact authorization details to be added.

For IP or IP ranges, there can be two data sources: Reverse DNS and WHOIS, each of which can return results independently. 

The Reverse DNS technique looks at the hostnames of the IPs in the range; and if they're all in the same domain (according to known top-level domains), it will "authorize" postmaster@domain.com and abuse@domain.com. Additionally, if more parts of the domain are consistent on all tested IPs, it will authorize the first subdomain, for example, postmaster@sub.domain.com and abuse@sub.domain.com. Because it samples the IPs within the range, to guarantee sufficient accuracy, the largest range this data source can be used with is a /23, or about 500 IPs.  

The WHOIS approach queries global, regional, and national IP registrars, such as ARIN (American Registry for Internet Numbers) and APNIC (Internet address registry for the Asia-Pacific region), using the first IP in the range to find the most specific allocation record covering it. 

Once the allocation record is found, It then looks to make sure the range being requested isn't larger than the record covers. If this is the case, it authorizes any email addresses contained in the record. In order to allow access to as many appropriate parties as possible, the process will also include any authorization addresses for the ASN, a unique identifier that allows its autonomous system to exchange routing information with other systems. ( that "owns" the IP or range according to the paragraph below, as long as only one ASN is associated with it.

  • List of DKIM domains and access to their postmaster@ email addresses.


The domains that are d= should be added to the Feedback look form. Then the confirmation email shall be sent to the postmaster@domain address to authorize the reporting access.

Once the above is done you can use the following websites to register with the main free FBL providers (the most valuable/accessible):

  - FBL Universal

  - Outlook

  - Yahoo

  - SpamCop

Extra Postmaster data, also includes complaints info via the UI.

  - Google Postmaster
  - SNDS
  - Mail.ru
  - Seznam


Once it is done you will start receiving the FBLs.


Why is it important?

It is always important to keep a two-way communication with your subscribers. Complaint/FBL is one of those channels that will help you understand and analyze which senders, campaigns, and lists are sending more/less engaged emails as well as give a better understanding of sending email strategy and audience reactions to your email behaviors.

About the Author


Sergey Syerkin

Sergey has exceptional knowledge when it comes to email and deliverability from a compliance and operational perspective. With over 13 years of experience, he is now working on expanding his own monitoring product, EmailConsul, in order to ensure all senders have the data they need to make the right decisions.

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