Best practices to prevent email subscription form abuse

Understanding email form abuse

Email form abuse occurs when unauthorized users exploit website forms such as email subscription, contact us, and refer a friend. These unauthorized users send spam, phishing, or other unsolicited communications through the form's host system. Bad actors can also perform Distributed Denial of Service (DDoS) incidents on email sign-up forms and potentially overwhelm the server, making it unavailable to legitimate users. When left unprotected, these incidents can occur through website forms as third parties use email sending capabilities for their own purposes.

AWS doesn’t proactively notify you of email form abuse incidents. Without a monitoring mechanism in place, you likely notice these incidents through a spike in your bounce or complaint rate metrics in your Amazon SES sending metrics. When either of these rates exceed certain thresholds, AWS might limit or completely pause your ability to send emails.

To avoid these scenarios, proactively secure your sign-up forms and continuously monitor your sending metrics in the Amazon SES console. For more information, see Monitoring your Amazon SES sending activity and Monitoring your Amazon SES sender reputation.

How email form abuse operates

Email form abuse manifests through several technical indicators:

• Bounce rate increases: When bots submit not valid or nonexistent email addresses, your bounce rate spikes as emails fail to reach their intended recipients.

• Complaint rate spikes: Recipients who receive unsolicited emails through your compromised forms might mark them as spam. These markings increase your complaint rate.

• Volume anomalies: Sudden increases in form submissions or email sending volume might indicate automated bot activity rather than organic user growth.

• Geographic patterns: Unusual submission patterns from specific geographic regions or IP address ranges can signal coordinated abuse attempts.

Email form abuse prevention best practices

To prevent email form abuse, follow these best practices.

Implement CAPTCHA

CAPTCHA is a test that’s designed to determine whether an online user is a human or bot. This mechanism helps reduce the number of spam submissions and prevent bots from submitting requests on your form.

Establish a double opt-in process

With double opt-in, a user submits their email address into your form and then receives a confirmation email with a link. After they open that link and confirm their subscription, that user is added to your email list. This process prevents bots and spammers from automatically filling out forms with fake or disposable email addresses.

Double opt-in also creates a clean email list, and helps maintain a good sender reputation that’s crucial for email deliverability. This process adds an extra verification step that confirms that the email address is valid and the subscriber wants to receive your communications. The confirmation email must clearly explain what the subscriber is confirming and what type of content they can expect to receive. For more information, see Optimizing email deliverability: A user-centric approach to list management and monitoring.

Rate limiting

Rate limits set a maximum number of requests, such as sign-up attempts, that a user or client can make within a given timeframe, such as seconds, minutes, or hours. The mechanism tracks the number of sign-up attempts from each IP address or device. A threshold, such as 3–5 sign-up attempts per hour per IP address or 10–20 attempts per day per IP address, defines the maximum number of attempts allowed within a specific timeframe.

When you exceed the threshold, subsequent sign-up attempts from that IP address or device are blocked or delayed until the rate limit resets. This approach stops bots and bad actors from creating fake accounts or overwhelming the system with sign-up requests.

Other common types of rate limiting strategies include:

• User-based limiting: Limits the number of requests that a user can make, usually by tracking an IP address or API key.

• Geographic limiting: Limits requests based on the user's geographic location.

• Server-based limiting: Limits the number of requests that a server can handle to maintain performance.

Restrict custom user content

This strategy focuses on what you allow users to input into your forms. If you allow unrestricted input, then bad actors and bots can easily abuse your forms. They often use free-text fields to inject spam content, links, or harmful code into your email list. This type of abuse can damage your reputation and deliverability.

Minimize the number of fields on your sign-up form to only those that you require for legitimate sign-ups, such as email address and name. Additionally, use email validation to verify that the email address entered is in a valid format and that the domain exists. This approach blocks unauthorized users from adding targeted content into open text fields and limits input to valid email addresses only.

Benefits of implementation

Implementing these email form abuse prevention measures provides multiple advantages to your organization:

• Improved sender reputation: By preventing spam and not valid email addresses from entering your system, you maintain higher deliverability rates and avoid being flagged by email providers.

• Cost reduction: Preventing abuse reduces unnecessary email sending costs and potential fees associated with high bounce rates or complaint rates.

• Enhanced user experience: Legitimate users receive relevant communications without being overwhelmed by spam. This measure can lead to higher engagement rates and customer satisfaction.

• Operational stability: Rate limiting and validation prevent automated requests from overwhelming your systems, maintaining consistent performance for legitimate users.

• Compliance protection: These measures help you maintain compliance with email marketing regulations and AWS Acceptable Use Policy requirements.

Conclusion

Although these measures reduce the risk of email form abuse incidents, there’s no method that can prevent all abuse from occurring. The benefits of following these guidelines far outweigh the time required to implement them. It's more effective to set up preventative measures than deal with the consequences of an email form abuse issue.

Review your current email form configurations and implement the preventative measures outlined in this article. To stay informed about evolving practices, visit the AWS Trust & Safety Center.