Summary
Gmail's stricter enforcement of RFC5322 standards compared to Outlook is the primary reason for bounces. The RFC5322 standard defines specific email header formatting rules. Common violations include duplicated or missing headers, incorrect character encoding, line ending inconsistencies, invalid syntax, and invisible characters. While Outlook may allow some flexibility, Gmail's stringent parsing rejects non-compliant emails. Troubleshooting involves validating headers with online tools, analyzing bounce messages for specific errors, ensuring correct email formatting, and adhering to Google Workspace's sending best practices. Implementing SPF, DKIM, and DMARC authentication helps mitigate these issues and improve deliverability.
Key findings
- RFC5322 Defines Standards: RFC5322 dictates specific email header formats and syntax.
- Gmail is Stricter: Gmail enforces RFC5322 standards more rigorously than Outlook.
- Common Header Issues: Duplicated/missing headers, encoding problems, and line ending inconsistencies are frequent violations.
- Authentication is Key: SPF, DKIM, and DMARC are essential for authentication and mitigating RFC5322-related bounces.
Key considerations
- Header Validation: Always validate email headers using online tools before sending.
- Bounce Analysis: Carefully analyze bounce messages from Gmail for specific RFC5322 errors.
- Implement Authentication: Ensure proper implementation of SPF, DKIM, and DMARC to improve deliverability.
- Google's Best Practices: Adhere to Google Workspace's email sending best practices to avoid being marked as spam.
- Formatting Checks: Ensure correct email formatting, including valid character encoding and consistent line endings.
What email marketers say
11 marketer opinions
Gmail's stricter adherence to RFC5322 standards, compared to Outlook's more lenient interpretation, is the primary reason for email bounces despite Outlook acceptance. Common RFC5322 violations include duplicated headers, missing or malformed Date and From headers, incorrect character encoding, inconsistent line endings (CR/LF), and invisible characters. Online header validators and email testing tools are recommended for identifying and correcting these issues. Proper email formatting, analyzing bounce messages, and implementing DKIM and DMARC can also help mitigate RFC5322-related problems.
Key opinions
- Strictness: Gmail is stricter than Outlook in enforcing RFC5322.
- Common Errors: Duplicated headers, missing headers, incorrect encoding, line ending issues, and invisible characters are common RFC5322 violations.
- Validation: Online header validators and email testing tools help identify RFC5322 errors.
Key considerations
- Header Checks: Thoroughly validate email headers for RFC5322 compliance before sending.
- Testing: Utilize email testing tools to simulate Gmail's email parsing to identify potential issues.
- Implementation: Implement DKIM and DMARC to enhance email authentication and reduce the risk of rejection by Gmail.
- Bounce Analysis: Analyze bounce messages from Gmail to pinpoint specific RFC5322 violations.
Marketer view
Marketer from Email Geeks explains that RFC5322 specifies that some headers are only allowed to appear once, and suggests checking for malformed messages with duplicated headers.
7 Mar 2024 - Email Geeks
Marketer view
Marketer from Email Geeks asks where and how the headers were validated and explains that Outlook may not enforce RFC5322 fully but Gmail does, even more so.
20 Sep 2021 - Email Geeks
What the experts say
3 expert opinions
Gmail often enforces RFC5322 standards more rigorously than Outlook. Experts suggest the problem often lies with the sender's email construction, specifically within the email headers. Troubleshooting involves carefully examining headers for compliance, utilizing parsing and validation tools, and understanding that email providers interpret RFCs differently, resulting in varied acceptance.
Key opinions
- Gmail's Strictness: Gmail enforces RFC5322 more strictly than Outlook.
- Sender-Side Issue: The problem often originates from the sender's non-compliant email construction.
- Header Examination: Careful examination and validation of email headers are crucial for identifying and correcting RFC5322 violations.
Key considerations
- Header Validation: Always validate email headers against RFC5322 standards.
- Tool Usage: Utilize header parsing and validation tools to identify errors.
- Provider Differences: Recognize that different email providers may interpret and enforce RFC5322 differently.
Expert view
Expert from Word to the Wise shares tips on troubleshooting email headers, including using tools to parse and validate headers, looking for common errors like missing or malformed fields, and understanding that different email providers may interpret the RFCs differently.
11 Jun 2022 - Word to the Wise
Expert view
Expert from Email Geeks asks if the user has looked at the headers they are sending and if they are sending 5322 compliant mail, suggesting the issue is likely on their end.
10 Dec 2022 - Email Geeks
What the documentation says
5 technical articles
RFC5322 defines precise email header formatting rules which Gmail strictly enforces. Deviations from these specifications, including incorrect syntax, line lengths, character usage, or missing required headers, can lead to email rejection. While Outlook may allow some flexibility, Google Workspace Admin documentation emphasizes adherence to best practices and proper authentication (SPF, DKIM, DMARC). Implementing DKIM can also mitigate RFC5322 issues by ensuring header integrity. Overall, strict compliance with RFC5322 is critical for deliverability to Gmail.
Key findings
- RFC5322 Definition: RFC5322 defines the strict formatting rules for email headers.
- Gmail Enforcement: Gmail strictly enforces RFC5322 specifications.
- Outlook Flexibility: Outlook may allow some deviations from RFC5322 for usability.
- Mitigation with DKIM: Proper DKIM implementation can help mitigate RFC5322-related issues by ensuring header integrity.
Key considerations
- Adherence to RFC5322: Strictly adhere to RFC5322 specifications when formatting email headers.
- Email Address Syntax: Ensure email addresses conform to IETF's syntax rules.
- Authentication Protocols: Implement proper authentication (SPF, DKIM, DMARC) to improve deliverability.
- Google Workspace Guidelines: Follow Google Workspace's email sending best practices.
Technical article
Documentation from RFC Editor explains that RFC5322 specifies the exact format for email headers, including the use of specific characters, line lengths, and the presence of required headers. Deviation from these specifications may lead to non-compliance and potential rejection by email servers like Gmail.
5 Jan 2025 - RFC Editor
Technical article
Documentation from DKIM.org explains that properly implementing DKIM can help mitigate RFC5322 related issues, as DKIM signs email headers, ensuring they haven't been tampered with and meet certain standards.
15 Feb 2023 - DKIM.org
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