Summary
Apple X-Headers are non-standard email header fields that provide insight into the filtering decisions made by email providers, especially Apple. They're similar to Microsoft headers and indicate actions like moving emails to the inbox or junk folder. These headers contain proprietary information such as spam scores (like X-ICL-Score) and classifications (CLX, potentially from Proofpoint or Cloudmark). They allow for custom filtering rules, internal routing, security scanning details, and can be used to track deliverability issues, marketing campaign performance, and potential phishing attempts. X-headers reveal how email is categorized and processed, but their implementation varies across providers, requiring careful interpretation.
Key findings
- Filtering Decisions: X-Headers indicate the filtering decisions made, such as moving emails to the inbox or junk folder.
- Spam Evaluation: Headers like X-ICL-Score reveal how Apple's system evaluates email for spam.
- Custom Filtering: X-Headers enable developers to implement custom filtering rules.
- Security Insights: They provide details of security scans and can indicate phishing attempts.
- Deliverability Tracking: X-Headers help track deliverability issues and campaign performance.
- Proprietary Classifications: X-headers contain proprietary classifications, such as CLX from Proofpoint.
- Non-Standard Header: X-Headers are non-standard additions to email headers, used for filtering and categorisation.
Key considerations
- Implementation Variance: The implementation and interpretation of X-Headers vary across email providers.
- Proprietary Nature: Understanding proprietary implementations is crucial for accurate interpretation.
- Potential for Manipulation: X-Header data may be manipulated, requiring careful validation.
- Limited Standardisation: The X-headers being non-standardised, means they are not universally recognised, making reliance on them for critical functionality risky.
What email marketers say
10 marketer opinions
Apple X-Headers provide insights into email filtering decisions made by Apple's systems, including spam classification, routing, and security scanning. They are non-standard headers used to add custom information to email messages, which are then used to filter and categorize emails.
Key opinions
- Spam Filtering Insight: X-Apple headers, such as X-ICL-Score and X-Apple-Action, reveal how Apple evaluates emails for spam and the resulting actions.
- Custom Filtering Rules: X-headers facilitate custom email filtering based on specific criteria like tagging or routing messages, commonly utilized in custom email solutions.
- Internal Routing: X-headers can dictate internal email routing within provider infrastructures, enabling tailored delivery paths and enhancing management efficiency.
- Security Scanning Details: X-headers show email security scan results, indicating malware presence and providing insight into email security levels.
- Deliverability Issues: X-headers expose deliverability issues, including server information, bounces, and feedback loops, affecting email placement.
- Campaign Tracking: X-headers track marketing campaign performance through embedded identifiers, linking emails to specific campaigns for detailed analytics.
- Phishing Detection: X-headers may signal phishing attempts by revealing suspicious domains or sending patterns, acting as threat indicators.
- CLX Classifications: Some X-headers contain CLX classifications from Proofpoint, categorizing emails based on threat levels, content, and source reputation.
Key considerations
- Implementation Specificity: X-header implementations vary across email providers and systems, requiring understanding of each implementation for accurate interpretation.
- Non-Standard Nature: Being non-standard headers, X-headers are not universally recognized, making reliance on them for critical functionality risky.
- Data Integrity: The data within X-headers may be manipulated or spoofed, necessitating careful validation to prevent misuse.
- Privacy Concerns: X-headers can expose sensitive information about email filtering processes and security measures, raising privacy and security concerns if improperly handled.
- Constant Evolution: The meanings of X-headers can change over time, making it important to stay updated.
Marketer view
Marketer from Email Geeks assumes that CLX is based on cloudmark or proofpoint.
11 Nov 2024 - Email Geeks
Marketer view
Email marketer from EmailGeek Forum mentions that X-Apple headers, like `X-ICL-Score`, give insight into how Apple's system evaluates email for spam. A higher score means a greater chance the email is spam.
26 Jan 2024 - EmailGeek Forum
What the experts say
4 expert opinions
Apple X-Headers, similar to MSFT headers, indicate filtering decisions (e.g., INBOX, Junk). These headers, including X-CLX-Whatever, have been used by iCloud for spam filtering metadata for a while. Email providers and filtering systems use them to add proprietary information, such as spam scores and classification rules, to identify spam based on sender reputation, spam checks, and classification reasons.
Key opinions
- Filtering Indicators: Apple X-Headers indicate filtering decisions, similar to Microsoft headers.
- Historical Usage: iCloud has used X-CLX-Whatever headers for spam filtering metadata.
- Proprietary Information: Email providers use X-Headers to add proprietary information about email filtering.
- Spam Identification: X-Headers store data to identify spam based on sender reputation, spam checks, and classification reasons.
Key considerations
- Contextual Interpretation: The meaning and usage of X-Headers can vary significantly between different email providers and systems.
- Proprietary Nature: Understanding the specific proprietary implementations is essential for accurately interpreting the information contained within X-Headers.
- Reliability: X-Headers should not be solely relied upon for critical decisions, as they are non-standard and subject to manipulation or misinterpretation.
Expert view
Expert from Spam Resource mentions that X-headers are used to store data and can be used to identify spam. Different X-headers can indicate a sender's reputation, the results of spam checks, or the reasons why a message was classified as spam.
21 Oct 2023 - Spam Resource
Expert view
Expert from Email Geeks shares that the Apple X-Headers are similar to MSFT headers and indicate the filtering decision on the message, providing examples for both INBOX and Junk folders.
16 Dec 2024 - Email Geeks
What the documentation says
4 technical articles
Apple X-Headers are non-standard header fields used for custom email information. `X-Apple-MoveToFolder` indicates the destination folder, while `X-Apple-Action` specifies the action taken. Some X-headers contain CLX classifications, revealing how Proofpoint categorizes emails by threat level, content, and source reputation. `X-Spam-Flag` indicates if an email is marked as spam by SpamAssassin.
Key findings
- Folder Destination: `X-Apple-MoveToFolder` specifies the destination folder for an email.
- Action Specification: `X-Apple-Action` specifies the action taken on an email.
- CLX Classifications: Some X-headers contain CLX classifications, revealing Proofpoint's categorization process.
- Spam Identification: `X-Spam-Flag` indicates if an email has been marked as spam by SpamAssassin.
- Non-standard Header: X-headers are non-standard additions to email headers, used for filtering and categorisation.
Key considerations
- Non-Standard Usage: X-headers are non-standard, meaning their implementation and interpretation may vary.
- Provider Specificity: The specific meaning of X-headers often depends on the email provider or filtering system.
- Data Reliability: The information contained in X-headers may not always be accurate or reliable.
Technical article
Documentation from Proofpoint Communities explains that some X-headers contain CLX classifications, revealing how Proofpoint's technology categorizes emails based on threat levels, content, and source reputation.
2 Sep 2021 - Proofpoint Communities
Technical article
Documentation from SpamAssassin Wiki says X-Spam-Flag is a common header used to signify whether an email has been marked as spam by the SpamAssassin filtering system.
12 Aug 2023 - SpamAssassin Wiki
