Summary
Challenge-response systems have numerous negative impacts on senders and third parties. These include: inconveniencing innocent third parties via backscatter from forged addresses; negative impacts on email deliverability, as legitimate recipients may not complete challenges and providers may classify emails as spam; creation of a poor user experience due to added friction; non-compliance with SPF, leading to deliverability problems; potential server overload in high-volume situations; accessibility issues for users with disabilities due to CAPTCHAs; negative impacts on SEO; and a generally unfavorable perception as a spam filtering technique. Some individuals may even 'outsource' their spam filtering by simply approving all challenge responses.
Key findings
- Third-Party Inconvenience: Innocent third parties can be inconvenienced via backscatter when spammers use forged addresses.
- Deliverability Impact: Challenge-response systems negatively impact deliverability, with legitimate emails often lost and providers classifying such emails as spam.
- Poor User Experience: These systems create a poor user experience due to added friction and inconvenience.
- SPF Non-Compliance: Challenge-response systems often violate SPF, leading to deliverability problems.
- Server Overload: In high-volume situations, servers can be overloaded due to the processing demands of challenge-response systems.
- Accessibility Issues: CAPTHCHAs in challenge-response systems can create accessibility issues for people with disabilities.
- SEO Impact: Challenge response system causes a negative impact on SEO due to the systems inability to index the site, leading to lower search rankings.
- Backscatter Generation: Challenge-response systems often generate backscatter, flooding spoofed email address with unwanted challenge messages.
Key considerations
- Ethical Implications: Consider the ethical implications of potentially inconveniencing innocent third parties with backscatter.
- User Experience: Carefully evaluate the impact on user experience and potential loss of legitimate communications.
- Alternative Solutions: Explore alternative spam filtering techniques that do not rely on challenge-response mechanisms.
- System Capacity: Ensure server infrastructure can handle potential processing overloads in high-volume environments.
- Compliance: Check compliance with SPF to avoid deliverability problems.
- Accessibility: If a challenge-response system is used, prioritize accessibility for users with disabilities.
- Monitor SEO: Monitor how the use of challenge responses affects the SEO rankings.
What email marketers say
5 marketer opinions
Challenge-response systems negatively affect senders and third parties by impacting deliverability, creating poor user experiences, potentially overloading servers, and causing accessibility issues. Legitimate emails may be lost due to recipients not completing the challenges, and email providers often classify such systems as spam. The added friction deters communication, and CAPTCHAs can be difficult for users with disabilities.
Key opinions
- Deliverability Impact: Challenge-response systems negatively impact email deliverability. Legitimate emails might be lost due to uncompleted challenges, and email providers frequently classify such emails as spam.
- Poor User Experience: These systems create a poor user experience by adding friction and potentially deterring legitimate communication.
- Server Overload: In high-volume situations, challenge-response systems can overload servers due to the processing required for each blocked email.
- Accessibility Issues: Challenge-response systems create accessibility problems for people with disabilities because the CAPTCHAs are frequently difficult to read.
- False Positives: They increase the chances of false positives, meaning real emails are missed.
Key considerations
- Evaluate Alternatives: Consider alternative spam filtering methods that don't rely on challenging senders, such as more advanced content filtering or reputation-based systems.
- User Impact: Carefully weigh the potential negative impact on legitimate senders and recipients against the benefits of reducing spam.
- System Capacity: Ensure your server infrastructure can handle the processing load if implementing a challenge-response system, particularly in high-volume environments.
- Accessibility Compliance: If a challenge-response system is necessary, ensure it complies with accessibility guidelines to accommodate users with disabilities.
- Monitor Deliverability: Closely monitor deliverability rates and sender feedback to identify and address any issues caused by challenge-response systems.
Marketer view
Email marketer from Mailjet shares that if you are using a challenge-response system you are significantly hurting your deliverability with all major mailbox providers. It will also mean you are more likely to get false positives and your real emails missed.
3 Nov 2022 - Mailjet
Marketer view
Email marketer from StackExchange explains that challenge-response systems negatively impact deliverability. Legitimate recipients may not complete the challenge, leading to lost emails. Additionally, many email providers automatically classify emails from such systems as spam.
19 Sep 2021 - StackExchange
What the experts say
4 expert opinions
Challenge-response systems can negatively affect senders, third parties, and even SEO. They may inconvenience innocent third parties through backscatter from forged addresses, and some individuals deal with these challenges by simply approving them, essentially outsourcing spam filtering. Furthermore, they can hinder search engine indexing, leading to lower search rankings, and are often viewed unfavorably.
Key opinions
- Third-Party Inconvenience: Challenge-response systems can inconvenience innocent third parties through backscatter when spammers use forged sender addresses.
- Outsourced Spam Filtering: Some individuals opt to approve all challenge responses, effectively outsourcing their spam filtering to the senders.
- SEO Impact: Challenge-response systems can negatively impact SEO by preventing search engine crawlers from indexing the site, leading to lower search rankings.
- Negative Perception: Challenge/response filtering is generally viewed unfavorably.
Key considerations
- Ethical Implications: Consider the ethical implications of potentially inconveniencing innocent third parties with backscatter.
- Impact on Relationships: Think about the impact on relationships with legitimate senders who may be deterred by the challenge-response process.
- SEO Trade-offs: Weigh the SEO disadvantages against the benefits of reducing spam when deciding whether to implement a challenge-response system.
- Alternative Solutions: Explore alternative spam filtering methods that do not rely on challenge-response mechanisms.
Expert view
Expert from Word to the Wise explains that challenge response systems can hurt SEO because search engine crawlers will not fill out the challenge and therefore cannot index the site. This can result in lowered search engine rankings.
10 Sep 2022 - Word to the Wise
Expert view
Email marketer from Email Geeks explains that using challenge response systems can inconvenience innocent third parties if the original sender used a forged address.
20 Jan 2024 - Email Geeks
What the documentation says
3 technical articles
Challenge-response systems negatively affect senders and third parties through backscatter and SPF non-compliance. Backscatter floods innocent, spoofed sender addresses with unwanted challenge messages, while SPF non-compliance arises from forwarding mail from different IP addresses, invalidating SPF checks and causing deliverability issues.
Key findings
- Backscatter Generation: Challenge-response systems often generate backscatter, flooding innocent, spoofed sender addresses with unwanted challenge messages.
- SPF Non-Compliance: Challenge-response systems frequently violate Sender Policy Framework (SPF) because they forward mail from a different IP address than the original sender, thus invalidating SPF checks.
- Poor Filtering Technique: Challenge-response is considered a poor filtering technique because it bounces spam back to forged sender addresses (backscatter).
Key considerations
- Impact on Third Parties: Consider the negative impact on third parties who may receive unwanted backscattered emails.
- Deliverability Risks: Evaluate the deliverability risks associated with SPF non-compliance when using challenge-response systems.
- Alternative Spam Filtering: Explore alternative spam filtering techniques that don't rely on challenge-response mechanisms to avoid backscatter and SPF issues.
Technical article
Documentation from Microsoft Learn explains that challenge/response systems often generate backscatter. Backscatter occurs when a spammer spoofs the sender address for a message, and the challenge/response system sends a challenge message to the innocent, spoofed sender address, flooding them with unwanted email.
2 Aug 2021 - Microsoft Learn
Technical article
Documentation from RFC explains the challenge response system does not comply with Sender Policy Framework (SPF). SPF helps prevent sender address forgery and relies on the sending server's IP address. Challenge-response systems often forward mail from a different IP address, invalidating the SPF check and potentially causing deliverability problems.
4 Apr 2024 - RFC-4408
Are abuse reports and feedback loops (FBLs) still useful in email marketing, and how do they work with different email clients?
Can 'invalid recipient' bounce messages be false positives and what should I do about it?
How are bad actors using Google Forms to send spam?
How are Gmail and Yahoo enforcing unsubscribe requests, and what factors do they consider for compliance?
How can I avoid Gmail security warnings on emails?
How can I effectively avoid spam filters when sending emails?
How can I identify and prevent spam/bot traffic at email subscription points?
How can spam complaints and bad content choices impact email deliverability?
How do bounces and phishing attacks affect email deliverability and domain reputation?
What are common Gmail deliverability myths and how can they be avoided?
What are the CAN-SPAM and CASL requirements for unsubscribe confirmation pages, preference updates, and email re-entry?
Why are my emails landing in spam even though they pass SPF, DKIM, and DMARC?
