How to investigate Gmail evidence
Gmail troubleshooting usually spans two evidence layers: the message-level rejection or header and the domain-level authentication state. Mailybox keeps those layers separate so a generic status code is not treated as the complete cause.
Signals worth checking
- SPF and DKIM authentication
- DMARC alignment
- Bounce and SMTP diagnostic text
- List-Unsubscribe and campaign markup
- Message source size and clipping pressure
Diagnostic path
- Start with the complete SMTP rejection rather than the numeric code alone.
- Use the sending domain to verify public authentication and dependency state.
- Use a real delivered message header when the problem involves alignment, forwarding or route-specific behavior.
- Preflight promotional HTML separately from domain authentication.
Questions this hub can answer
- Why did Gmail reject this message?
- Does the sending domain satisfy authentication prerequisites?
- Is the message at risk of clipping?
- Did forwarding alter authentication evidence?
Provider documentation
Use the provider’s own documentation for the current provider-defined policy or error meaning, then verify the actual configuration with the tools below.