Read the delivery failure before acting
A bounce is a delivery failure reported during or after a send. Marketing platforms commonly distinguish hard bounces, usually permanent failures, from soft bounces, usually temporary ones. These labels are summaries; use the SMTP reply, enhanced status and provider policy to understand what actually happened.
A temporary 4xx SMTP reply asks the sending system to try later. A permanent 5xx reply rejects that attempt. A 5xx policy or authentication rejection does not automatically mean the recipient mailbox is nonexistent. Keep address problems separate from sender problems.
A triage sequence
- Capture the evidence: recipient domain, timestamp, SMTP reply, sending stream and campaign. Avoid copying unnecessary personal data into tickets.
- Determine scope: one contact failing suggests a different investigation from most contacts at the same provider failing together.
- Find the cause: distinguish a nonexistent recipient from full storage, rate limiting, authentication or reputation policy.
- Apply the sending platform's rule: confirm how it retries temporary failures and when it suppresses repeated failures.
- Record the resolution: update the contact status or fix the sender configuration, keeping suppression history intact.
Three illustrative failures
Recipient rejected: a server reports that the mailbox does not exist. Verify spelling, then suppress the confirmed invalid address. Do not re-import it as a fresh contact next week.
Temporary deferral: a receiving provider slows the sender. Let the sending platform manage retries; do not launch a second campaign to the deferred group. Investigate sending pace and reputation if the pattern persists.
Authentication rejection: many recipients reject mail from one sending stream. Review authentication and the full reply before removing valid contacts. Verification of recipients cannot repair the sender's DNS or DKIM signing.
Measure causes separately
Track permanent recipient failures, temporary failures and policy rejections by provider and collection source. Define the denominator: attempted recipients, accepted messages or a platform-specific campaign total. Comparing percentages from different denominators can hide the actual change.
Verification before a campaign helps find mailbox risks, while bounce processing learns from real delivery. Neither replaces the other. Keep unsubscribe, complaint and hard-bounce suppression rules authoritative even when a later verifier reports valid.