What data sources should I check first? (e.g., bounces, complaints, Postmaster Tools)

Data source priority for diagnosis:

• 1. Postmaster Tools (Gmail, SNDS)
• Current reputation status
• Authentication pass rates
• Spam rate data
• 2. Bounce logs
• Error codes reveal block reasons
• Pattern changes indicate new problems
• 3. Complaint data
• Feedback loop reports
• Timing and source of complaints
• 4. Blocklist checks
• MXToolbox, Spamhaus, Barracuda
• IP and domain separately
• 5. Engagement metrics
• Opens, clicks by provider
• Changes over time
• 6. Sending logs
• Volume changes
• List composition changes
• Start with reputation indicators, then dive into specifics.
• Check the harbor status board first, then inspect the cargo manifest.