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In recent years, the daily volume of emails has exceeded an astounding three hundred billion, surpassing the number of people living on Earth by a factor of approximately forty. It's undeniable that within this massive quantity of emails, a significant portion consists of unwanted mail known as spam. Spam encompasses a wide range of unsolicited messages, spanning from annoying promotional offers to potentially dangerous scams and phishing attempts. 

This article aims to offer a comprehensive overview of email spam complaints, exploring their lifecycle and their profound impact. 


Sender or Email sender refers to a brand or organization that sends emails to their recipients. They can manage their own email infrastructure, including sending servers, or they can send emails with the help of a 3rd party – Email service provider. 

Email service provider or ESP is a company that offers email marketing and/or email delivery services on behalf of brands or organizations. They provide the necessary infrastructure, tools, and expertise to manage and deliver email campaigns effectively.  

Email spam complaints 

Spam filters work by analyzing the email content, the sender's security and the domain/IP reputation. These filters employ various techniques to identify and classify emails as spam or legitimate messages. Factors such as suspicious keywords, presence of certain attachments, or known malicious links can trigger the spam filters. Additionally, the reputation of the sender's domain or IP address plays a role in determining the likelihood of the email being marked as spam. By considering these elements, spam filters aim to automatically separate unwanted messages from legitimate ones. 

However, no matter how clever technology gets, recipients are the ones who know what emails they expect, have signed up for, or trust. Most mailbox providers offer a spam reporting feature, typically in the form of a spam button. When users click this button, a spam complaint is registered, and the message in question and all future correspondence from the same sender are automatically redirected to the spam/junk folder of this mailbox. Interestingly, even legitimate marketers may find their messages marked as spam due to certain factors. These can include overly frequent promotional content, the absence of a properly working unsubscribe option, sudden emails to users who have been inactive for an extended period, or even the inclusion of incorrect email addresses in the lists, perhaps due to the absence of Double Opt-in. 

Feedback loops 

A Feedback Loop (FBL) serves as a valuable two-way communication channel between email senders and mailbox providers. It allows mailbox providers to inform senders when recipients mark their emails as spam. When a user clicks the spam button, an FBL report is generated and sent back to the original sender or their Email service provider. Senders can either subscribe to FBL programs directly and manage the feedback loops themselves, or subscribe through their ESP. For example, SAP Emarsys includes FBL subscriptions by default. 

While each mailbox provider may have its own specific guidelines and requirements for managing feedback loops, many of them emphasize the importance of suppressing recipients who have previously complained.  

A powerful relationship  

By reporting spam, users not only protect themselves from unwanted emails, but they also play a crucial role in the broader fight against spam. User-generated spam complaints help educate and refine the algorithms that power email filtering systems. Furthermore, a high rate of spam complaints can have a significant impact on the deliverability of emails from even legitimate senders, emphasizing the importance of addressing spam concerns at both an individual and collective level. Feedback loops play a vital role in it.  

Feedback loops offer valuable insights to senders, enabling them to identify potential issues and patterns that may contribute to spam complaints. This valuable feedback allows senders to take prompt corrective measures, thereby actively managing their email reputation. Additionally, for email service providers, FBLs are an effective tool in identifying and isolating risky clients to protect their infrastructure. 

Issues and challenges of the FBL process 

The implementation of feedback loops is a vital component of the email ecosystem, but it's essential to acknowledge and address certain challenges and concerns associated with their usage. 

One key challenge is that not all mailbox providers offer feedback loop programs to senders. For instance, Gmail does not currently provide an opportunity to identify a complainant, which limits the comprehensiveness of available data for senders and ESPs. Considering Gmail's significant user base, this can impact the effectiveness of feedback loop data in providing a complete picture. While Gmail currently provides only aggregate FBL reports, it is reasonable to expect that it follows similar patterns as other mailbox providers. For instance, if Yahoo and Microsoft experience a high number of complaints, it is likely that Gmail also has a similar level of complaints. Although the specific complaint data for Gmail may not be available, observing trends among other major providers can provide insights into the overall complaint landscape. 

The General Data Protection Regulation (GDPR) and other data privacy regulations impose strict requirements on the collection, processing, and storage of personal data. Feedback loop data may contain personally identifiable information of complainants. Proper measures must be taken to ensure that feedback loop data is handled in accordance with applicable data protection laws. 

Some senders may misuse feedback loop reports by proactively reaching out to complainants. While the intention may be to resolve issues, this approach can be seen as intrusive or unwanted by recipients, potentially leading to a negative user experience. It is crucial for senders to respect user preferences and privacy, ensuring that contact with complainants is done in a responsible and ethical manner. 

By recognizing these challenges, senders can harness the benefits of feedback loops while addressing concerns related to availability, data privacy, and user experience. 


What’s next? 

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You can ask questions and provide suggestions for helpful email deliverability topics in the Q&A area Q&A – SAP Emarsys Email Deliverability. 

And if you’d like to find out more SAP Emarsys, you can visit the community page: SAP Emarsys CX.