Free tool
Bounce Message Decoder
Paste the raw bounce or rejection message you got back – including the SMTP code, brackets, and whatever link it points to. This reads Gmail, Outlook, and Yahoo's actual wording, not a generic code lookup table, so you get a diagnosis tailored to what that specific provider is actually telling you.
Paste a bounce message first – there's nothing here to diagnose yet.
Nothing is sent anywhere – this runs entirely in your browser.
What to check first
This reads the exact wording Gmail, Outlook, and Yahoo use in their bounce messages, matched against known patterns – it's a diagnostic aid, not a guarantee. Bounce phrasing changes over time and varies by sending platform, so treat this as a strong starting point and confirm against the provider's own postmaster documentation before making infrastructure changes.