What technical issues most often masquerade as reputation problems?

Authentication failures:

• Broken SPF causing delivery failures
• DKIM signature errors
• DMARC misalignment
• Looks like: sudden delivery drop, spam placement

DNS issues:

• Expired or changed records
• Propagation problems
• SPF lookup limit exceeded
• Looks like: inconsistent delivery, authentication failures

Infrastructure problems:

• IP address changes
• TLS certificate issues
• Server configuration changes
• Looks like: blocks, deferrals

Diagnosis priority:

• Check technical issues first (faster to identify)
• Then investigate reputation
• Technical issues are usually faster to fix
• Check if the ship is mechanically sound before assuming the harbor banned it.