Summary
ISPs employ a multi-layered approach to identify and handle suspicious email, focusing on sender reputation, email authentication, user feedback, content analysis, and list hygiene. They monitor sender reputation using metrics like bounce rates, complaints, and engagement. Email authentication protocols (SPF, DKIM, and DMARC) are crucial for verifying sender identity and preventing spoofing. User feedback, including complaint feedback loops (FBLs), helps ISPs identify and address spam. Content analysis involves scanning for spam-like keywords, phrases, and formatting. Spam traps are used to identify senders with poor list hygiene. Monitoring sending volume and frequency, especially from new IPs, is also common. Senders are advised to maintain clean email lists, implement proper authentication, monitor their reputation using tools like Google Postmaster Tools, and avoid spam triggers in their email content. Testing deliverability via seed lists is also recommended.
Key findings
- Sender Reputation is Key: ISPs heavily rely on sender reputation, based on factors like bounce rates, spam complaints, and engagement, to filter spam.
- Authentication Matters: Proper email authentication (SPF, DKIM, DMARC) is essential for verifying sender identity and improving deliverability.
- Spam Traps Detect Poor Hygiene: ISPs use spam traps to identify senders with poor list hygiene practices; hitting them can result in blacklisting.
- User Feedback is Important: ISPs use feedback loops (FBLs) to allow recipients to report spam, enabling senders to remove complainers.
- Content Analysis Detects Spam: ISPs analyze email content for spam-like keywords, phrases, and formatting.
- Volume Monitoring Protects Reputation: ISPs monitor sending volume, especially from new IPs, to prevent spam attacks.
- ISPs may share garbage IPs: Some ISPs may share lists of IPs known to send garbage mail.
Key considerations
- Prioritize List Hygiene: Regularly clean your email lists to remove inactive or invalid addresses and avoid spam traps.
- Implement Authentication: Implement SPF, DKIM, and DMARC to authenticate your emails and improve sender reputation.
- Monitor Your Reputation: Actively monitor your sender reputation using tools like Google Postmaster Tools to identify and address issues.
- Engage Your Audience: Focus on sending engaging content that encourages recipients to interact with your emails.
- Participate in Feedback Loops: Participate in feedback loops (FBLs) to identify and remove complainers from your lists.
- Optimize Your Content: Avoid spam triggers in your email content, such as excessive promotional language or poor formatting.
- Warm-up New IPs Gradually: Gradually increase sending volume when using new IPs to establish a positive reputation.
- Utilize Seed Lists: Leverage seed lists to proactively test deliverability and identify potential blocking issues
What email marketers say
10 marketer opinions
ISPs employ a multi-faceted approach to identify and handle suspicious email, focusing on sender reputation, content analysis, and recipient feedback. They monitor factors like bounce rates, spam complaints, and engagement metrics to assess sender trustworthiness. Techniques such as spam traps, feedback loops, and email authentication protocols (SPF, DKIM, DMARC) are used to detect and filter unwanted messages. Senders can improve deliverability by practicing good list hygiene, gradually increasing sending volume, and avoiding spam triggers in their email content.
Key opinions
- Sender Reputation: ISPs heavily rely on sender reputation, built from factors like bounce rates, complaints, and engagement, to filter spam.
- Spam Traps: ISPs use honeypots or spam traps to identify senders with poor list hygiene practices; hitting these can lead to blacklisting.
- Feedback Loops: Feedback loops (FBLs) allow recipients to report spam, enabling senders to remove complainers and improve deliverability.
- Email Authentication: Proper email authentication (SPF, DKIM, DMARC) is crucial for verifying sender identity and avoiding spam filters.
- Content Analysis: ISPs analyze email content for spam-like keywords, phrases, and formatting (e.g., excessive capitalization, exclamation points).
- Volume Monitoring: ISPs monitor sending volume and frequency, especially from new IPs; sudden spikes can trigger spam filters.
Key considerations
- List Hygiene: Regularly clean your email lists to remove inactive or invalid addresses and avoid spam traps.
- Authentication: Implement SPF, DKIM, and DMARC to authenticate your emails and improve sender reputation.
- Engagement: Focus on sending engaging content that encourages recipients to interact with your emails, signaling positive behavior to ISPs.
- Feedback Loops: Participate in feedback loops (FBLs) to identify and remove complainers from your lists.
- Content Optimization: Avoid spam triggers in your email content, such as excessive promotional language or poor formatting.
- Warm-up IPs: Gradually increase sending volume when using new IPs to establish a positive reputation.
Marketer view
Marketer from Email Geeks shares that some ISPs provide IPs that they have high confidence are garbage mail, and blocking them is acceptable. He also suggests adding a header to suspect messages to inform Mailbox Providers (MBPs) that the messages are spam.
29 Dec 2021 - Email Geeks
Marketer view
Email marketer from Litmus explains that ISPs use sophisticated spam filters that analyze various aspects of an email, including the sender's IP address, domain reputation, email content, and user engagement. They recommend senders to test their emails before sending, use a reputable email service provider (ESP), and monitor their deliverability metrics to identify and address any issues.
27 Jun 2023 - Litmus
What the experts say
4 expert opinions
ISPs employ various methods to identify and handle suspicious email, with a strong emphasis on sender reputation, recipient feedback, and list hygiene. They utilize spam traps to catch senders with poor list management practices. Reputation scoring systems are used to assess the trustworthiness of sending IPs and domains, influencing email acceptance or filtering. Monitoring Complaint Feedback Loops is crucial for understanding recipient reactions and mitigating deliverability problems. Seed lists provide a mechanism for proactively testing deliverability across different mailbox providers.
Key opinions
- Spam Traps: ISPs and blocklist providers use spam traps to identify senders with poor list hygiene, resulting in deliverability penalties.
- Reputation Scoring: ISPs assign reputation scores based on volume, complaints, and engagement to determine email acceptance or filtering.
- Feedback Loops: Participating in Complaint Feedback Loops (FBLs) is vital for understanding recipient reactions and removing complainers.
- Seed Lists: Seed lists allow for deliverability testing across different mailbox providers to identify potential blocking issues.
Key considerations
- List Hygiene: Maintain clean email lists to avoid hitting spam traps and negatively impacting sender reputation.
- Monitor Reputation: Actively monitor sender reputation to identify and address issues affecting deliverability.
- Implement FBLs: Participate in and monitor Complaint Feedback Loops to promptly remove complainers and improve deliverability.
- Test Deliverability: Use seed lists to proactively test deliverability and identify potential blocking issues before widespread sending.
Expert view
Expert from Spam Resource explains that ISPs and blocklist providers use spam traps (pristine and recycled) to identify senders with poor list hygiene practices. Hitting a spam trap indicates that the sender is either harvesting email addresses or not properly managing their list and can result in severe deliverability penalties.
11 Aug 2021 - Spam Resource
Expert view
Expert from Word to the Wise shares that seed lists can be used to test deliverability rates across different mailbox providers. By sending test emails to seed addresses, senders can identify potential blocking issues before widespread sending.
19 Apr 2022 - Word to the Wise
What the documentation says
4 technical articles
ISPs like Google and Microsoft employ a combination of user reports, spam traps, authentication failures (SPF, DKIM, DMARC), content filtering, sender reputation analysis, and machine learning to identify and block suspicious emails. RFC documents outline mechanisms for reporting unsolicited bulk email. DMARC.org emphasizes the importance of DMARC to identify and block fraudulent emails. Senders are advised to authenticate their emails, maintain clean sending lists, and monitor their reputation using tools like Google Postmaster Tools.
Key findings
- User Reports & Spam Traps: ISPs utilize user reports and spam traps as key signals for identifying suspicious emails.
- Authentication Protocols: Authentication protocols like SPF, DKIM, and DMARC are crucial for verifying sender identity and preventing spoofing.
- Content Filtering & Reputation: ISPs combine content filtering, sender reputation analysis, and machine learning to identify and block suspicious emails.
- UBE Reporting Mechanisms: RFC outlines mechanisms for reporting unsolicited bulk email to relevant administrators.
- DMARC for Fraud Prevention: DMARC helps ISPs identify and block fraudulent emails by ensuring proper authentication and providing reporting mechanisms.
Key considerations
- Implement Authentication: Ensure proper email authentication (SPF, DKIM, DMARC) to verify sender identity and prevent spoofing.
- Monitor Reputation: Actively monitor sender reputation using tools like Google Postmaster Tools to identify and address any issues.
- Maintain Clean Lists: Regularly clean email lists to remove inactive or invalid addresses and avoid spam traps.
- Follow Best Practices: Adhere to email sending best practices to avoid being flagged as spam by ISPs.
Technical article
Documentation from Google explains that Google uses various signals to identify suspicious emails, including user reports, spam traps, and authentication failures (SPF, DKIM, DMARC). They advise senders to monitor their reputation through Google Postmaster Tools and address any issues promptly to avoid being flagged as suspicious.
19 Dec 2021 - Google
Technical article
Documentation from Microsoft explains that their spam filters use a combination of technologies, including content filtering, sender reputation, and machine learning, to identify and block suspicious emails. They also provide guidance on best practices for senders to avoid being flagged as spam, such as authenticating emails and maintaining a clean sending list.
7 Jan 2022 - Microsoft
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