TABLE OF CONTENTS

RFC 5322 Non-Compliant Email Messages: Complete Troubleshooting Guide

What's Happening?

Your emails are being rejected by recipient servers because they don't meet the technical formatting standards required by RFC 5322 - the official specification that governs email format. These rejections occur when your email headers, sender addresses, or message structure violate established email protocols, causing receiving servers to refuse delivery entirely.

Quick Diagnosis: Identifying RFC 5322 Compliance Issues

Bounce Message Examples

  • "The email was rejected because the From header or domain does not meet required technical standards"
  • "The message was rejected due to protocol or formatting issues, causing the connection to be refused"
  • "The message was rejected due to a mail loop or excessive hops, violating email transmission standards"
  • "The sender address or message format does not meet email standards or is not accepted by the recipient server"
  • "The email message does not meet required formatting or header standards, such as missing or invalid From header or disallowed characters"
  • "The message was blocked due to content or attachments violating Gmail's security or content guidelines"
  • "The email message format or headers do not comply with required standards"
  • "The sender address format does not comply with email standards (RFC 5321/5322)"

Understanding RFC 5322 Compliance

Key Concepts

RFC 5322 Defines:

  • Proper email header structure and formatting requirements
  • Valid sender address formats and character restrictions
  • Message routing protocols and hop limitations
  • Required and optional header fields for email messages
  • Character encoding standards for international content

Common Compliance Violations

Header Issues:

  • Missing or malformed From header
  • Invalid characters in sender name or address
  • Improper date formatting in headers
  • Excessive or malformed Received headers

Address Format Problems:

  • Special characters not properly encoded
  • Missing angle brackets around email addresses
  • Invalid domain name formatting
  • Improper use of display names

Message Structure Issues:

  • Mail loops causing excessive hops
  • Line length violations (over 998 characters)
  • Missing required message boundaries

Step-by-Step RFC 5322 Compliance Resolution

Step 1: Audit All Sender Configurations

Instructions:

  1. Review Campaign Sender Settings:
    • Go to Marketing → Email → Campaigns
    • Open each campaign experiencing delivery issues
    • Click on the email step within your campaign
    • Review the "From Name" and "From Email" fields for proper formatting
  2. Check Workflow Email Actions:
    • Go to Automation → Workflows
    • Open workflows that include email actions
    • Click on each "Send Email" action in your workflow
    • Review sender name and email address configuration
  3. Audit Bulk Action Email Settings:
    • Go to Contacts → Bulk Actions
    • Review the sender name and email fields in bulk action setup
    • Ensure consistency with your authenticated sending domains
    • Verify that bulk email sender information matches campaign standards
  4. Standardize All Sender Information:
    • Ensure sender names contain only alphanumeric characters, spaces, and basic punctuation
    • Remove special characters like quotes, brackets, or symbols from sender names
    • Verify email addresses follow the format: name@domain.com without special characters
    • Keep display names under 64 characters
    • Use consistent sender name formatting across all email touchpoints
    • Ensure all sender email addresses are properly authenticated
    • Verify reply-to addresses are valid and properly formatted

Sender Configuration Success

  • All campaign sender addresses follow proper email format standards
  • Workflow email actions use consistent, compliant sender information
  • Bulk action emails maintain proper formatting and structure
  • Display names contain only standard characters across all email touchpoints

Step 2: Validate Email Template Structure

Instructions:

  1. Access email templates:
    • Go to Marketing → Emails → Templates
    • Open templates that are experiencing delivery issues
  2. Fix template compliance issues:
    • Verify that line lengths don't exceed 998 characters
    • Test templates across different email clients

Step 3: Use External Validation Tools


  1. Mail-Tester.com:
    • Send a test email from your campaign, workflow, or bulk action to the provided address
    • Review the detailed compliance report
    • Address any RFC 5322 violations identified
  2. MXToolbox Email Header Analyzer:
    • Copy email headers from a delivered message
    • Paste into the header analyzer tool
    • Review compliance warnings and errors
  3. RFC 5322 Validator Tools:
    • Use online RFC compliance checkers
    • Validate email address formats before importing contacts
    • Test message structure for standards compliance

Recovery Timeline and Expectations

Phase 1: Immediate Fixes (1-2 hours)

  • Action: Correct sender address formatting across campaigns, workflows, and bulk actions
  • Expected outcome: Immediate reduction in RFC compliance rejections

Phase 2: Template Optimization (2-4 hours)

  • Action: Review and fix all email templates for proper structure
  • Expected outcome: Elimination of message format violations

Phase 3: Validation and Testing (1-2 days)

  • Action: Comprehensive testing across all email sending methods
  • Expected outcome: Consistent delivery without RFC compliance issues

Prevention Best Practices

Ongoing Monitoring

  • Regular sender audits: Review sender information in campaigns, workflows, and bulk actions monthly
  • Template validation: Check all email templates for compliance before deployment
  • External testing: Use Mail-Tester.com weekly to catch issues early
  • Bounce monitoring: Watch for RFC compliance error patterns in delivery reports

Configuration Standards

  • Consistent sender information: Use the same compliant sender details across all email touchpoints
  • Standard character sets: Avoid special characters in sender names and display names
  • Proper email formatting: Always use valid email address formats
  • Template compliance: Ensure all HTML templates meet RFC standards

Still Having Issues?

If you continue to experience RFC 5322 compliance challenges:

  1. Document specific errors: Collect exact bounce messages and identify which sending method triggered them
  2. Test systematically: Send test emails from campaigns, workflows, and bulk actions separately
  3. Review recent changes: Check for any modifications to sender information or templates
  4. Cross-reference settings: Ensure consistency across all email sending methods in our platform