Why is Gmail bouncing my emails with RFC5322 errors when Outlook accepts them?

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.

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.

Email marketer from EmailGeeks Forum shares that common RFC5322 violations include missing Date or From headers, invalid character encoding, or incorrect line endings. These might not be flagged by all email clients but can cause issues with Gmail.

Email marketer from SendGrid explains implementing DMARC (Domain-based Message Authentication, Reporting & Conformance) can help address RFC5322 issues by providing a framework for email authentication and policy enforcement, reducing the likelihood of email rejection by Gmail.

Email marketer from EmailDrip Blog advises using online email header validators to check for RFC5322 compliance. These tools can highlight specific errors that might be causing Gmail to bounce the emails, which Outlook overlooks.

Email marketer from EmailOnAcid shares that ensuring your email formatting is correct, particularly in headers, can solve these RFC5322 issues. They recommend using their email testing tools before sending.

Email marketer from Reddit explains that sometimes, invisible characters or incorrect encoding in the headers can cause RFC5322 errors. These might not be immediately obvious, but Gmail's parser can detect them, while Outlook's might not.

Email marketer from SparkPost explains Analyzing bounce messages from Gmail can provide detailed information about the specific RFC5322 violation that caused the rejection, allowing for targeted troubleshooting.

Email marketer from Gmass blog shares you should use email testing tools. These tools can highlight specific errors that might be causing Gmail to bounce the emails, which Outlook overlooks. These tools can highlight specific errors that might be causing Gmail to bounce the emails, which Outlook overlooks.

Email marketer from Stack Overflow explains that Gmail is known to be stricter about RFC5322 compliance than Outlook. Outlook might be more forgiving of minor deviations, while Gmail strictly enforces the standard, leading to bounces.

Email marketer from Mailtrap Blog explains that RFC5322 requires specific use of Carriage Return (CR) and Line Feed (LF) characters for line endings in email headers. Inconsistent or incorrect usage of these characters can lead to RFC5322 errors, which Gmail may enforce more strictly.

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.

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.

Expert from Spam Resource explains that Gmail sometimes enforces RFC5322 more strictly, particularly regarding line endings and whitespace, compared to other email providers like Outlook. This strict enforcement can lead to bounces even if the email appears fine in Outlook.

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.

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.

Documentation from Microsoft clarifies that while Outlook strives for RFC compliance, it may implement certain relaxations or interpretations for usability, potentially allowing emails that Gmail would reject due to strict adherence to RFC5322.

Documentation from Google Workspace Admin details the importance of adhering to email sending best practices to avoid being marked as spam or violating RFC5322. This includes proper authentication (SPF, DKIM, DMARC) and respecting header formats.

Documentation from IETF mentions there are specific rules about email address syntax, including allowed characters and format. Non-compliance with these rules can lead to RFC5322 errors.