Email glossary · Practical guide
Hard bounce: classify the permanent failure before suppressing
Hard bounce commonly describes a permanent delivery failure. The label alone does not tell you whether the recipient address is invalid or the sender configuration caused the rejection.
Reviewed · Examples are illustrative
Who this helps: Readers checking a term before making an outreach or mailbox decision.
Meaning and common confusion
An invalid mailbox and an authentication rejection can both appear in failure reporting but require different repairs. Classify the full diagnostic before applying a recipient exclusion. Keep the message's failed outcome even when the operational cause is later corrected.
Worked example
This is a synthetic illustration, not a customer result or a live configuration to copy.
Failure A: recipient mailbox does not exist → review recipient suppression
Failure B: sender authentication rejected → repair sender configuration
Both failed; deleting the recipient list would not repair Failure B.Checks to make
- Read the enhanced code and explanatory text.
- Check affected scope before bulk suppression.
- Do not retry a confirmed invalid address without new verified evidence.
Next step and limits
Use the user-unknown and hard-bounce suppression guides for the relevant path. A generic bounce count is not a reliable diagnosis. Zintara's reported state should be interpreted alongside the provider evidence and the actual recipient record.
Source: Zintara product context for this operational definition
Source references
Worked examples are illustrative. Editorial procedures are suggested methods, not measured performance claims or promises of additional product features.
Related guides
- SMTP 550 user unknown: stop retrying an invalid destination →
- Hard-bounce suppression: classify evidence before retrying →