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Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →A bounce handler should suppress the recipient identified as failed in the delivery event—not the address that received the bounce, the visible From address, or the SMTP return path. Those addresses can serve different roles. Match each bounce to its original send, identify the failed recipient in the provider’s structured event, and classify the reason before changing suppression state.
Which address should a bounce handler suppress?
Suppress the recipient that the delivery failure names, if the failure warrants suppression. Keep that address separate from the message’s visible From, the SMTP envelope sender, and the return path.
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SMTP uses the reverse-path—the address commonly copied into Return-Path on final delivery—to designate where delivery errors should go. RFC 5321 describes its purpose as “to designate the address to which messages indicating non-delivery or other mail system failures are to be sent.” That destination can be a dedicated error mailbox or a service endpoint; it is not necessarily the recipient whose delivery failed. RFC 5321
If your handler suppresses the return-path or visible sender instead of the failed recipient, it can block future mail to a valid operational address while continuing to send to the address that actually failed.
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How to identify the failed recipient reliably
- Correlate the bounce with the original send. Use the provider’s event or message identifier and retain enough send context to connect delayed notifications to the correct delivery.
- Read the event’s recipient-level fields. Process the address listed as failed by the provider, not an address guessed from the message headers or notification destination.
- Classify the reason before changing recipient state. Review the bounce type, SMTP status, diagnostic text, event time, and sending identity when available.
- Update only the matching recipient record. Make repeated event processing safe so a duplicate or delayed event does not alter an unrelated address or overwrite a more recent state.
Amazon SES, for example, provides a bouncedRecipients list with an emailAddress, action, status, and diagnosticCode for each recipient. Its bounce object also classifies the outcome as Permanent, Transient, or Undetermined. Use those structured recipient details rather than inferring identity from headers. Amazon SES notification contents
When does a bounce justify suppression?
A delivery failure is evidence to interpret, not an automatic verdict that an address is invalid. A permanent rejection for a nonexistent mailbox or domain is a strong reason to stop sending to that recipient. A temporary failure may clear on its own. A rejection tied to content, authentication, policy, or sender reputation may call for fixing the message or sending setup—not suppressing a valid recipient.
- Permanent invalid-recipient failure: Stop future sends to the failed address, following the provider’s event classification and diagnostic details.
- Temporary condition: Avoid treating it as proof that the mailbox is invalid. The provider may retry, or a later send may succeed.
- Sender, content, or policy rejection: Investigate the cause on the sending side before deciding whether the recipient should be suppressed.
- Unclear or conflicting details: Preserve the raw diagnostic response and avoid turning a broad “hard bounce” label into an irreversible global block.
Bounce codes and accompanying explanations are not applied uniformly across receiving systems. M3AAWG discusses temporary failures and policy or reputation-related bounces as reasons to consider the details rather than rely on a generic label. M3AAWG recommendations for senders handling complaints Salesforce likewise warns that providers do not follow one standard and that temporary DNS or network problems can resemble permanent address failures. Salesforce: Enable Email Bounce Handling
Why delayed bounces require recipient-level tracking
Not every failure arrives while the original send is being attempted. A receiving server may accept a message and later send a delivery failure to the return path. This asynchronous bounce still needs to be matched to the original delivery and the recipient that failed; otherwise the handler may act on the wrong send or the wrong record.
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Retain the provider event or message identifier alongside the original recipient and sending identity. Process events idempotently—so receiving the same event again does not create a different suppression result—and apply changes to the specific recipient associated with that send. These are implementation safeguards, not universal SMTP rules; providers expose different correlation fields and event flows.
Provider policies are not SMTP rules
Providers differ in how they classify failures, deliver notifications, scope suppression, and expire entries. Their own policies are examples of service behavior, not requirements of the SMTP protocol.
| Provider | Recipient and failure details | Timing and suppression behavior |
|---|---|---|
| Amazon SES | Lists bounced recipients with email address, action, status, and diagnostic code; classifies bounce type as permanent, transient, or undetermined. AWS documentation | SES retries transient failures for a period before stopping; AWS advises removing a recipient after a permanent bounce. The exact retry duration is not stated on the cited page. |
| Cloudflare Email Service | Distinguishes account-level from sending-domain suppression scope; the sending-domain scope follows the sender identity for the sending method. Cloudflare documentation | Eligible soft-bounce suppressions default to 24 hours. Eligible permanent-rejection suppressions may expire after seven days or remain without expiry, depending on reason. Sender-side authentication or reputation failures do not create recipient suppressions. |
| Azure Communication Services | Maintains a managed suppression list for specified hard-bounce codes. Microsoft Learn documentation | A suppression lease can increase after repeated invalid-recipient attempts, up to a documented maximum of 14 days. |
| Salesforce | Processes delivery status notifications into contact, lead, or person-account status and marks a record bounced only for hard bounces. Salesforce Help | Documents both in-band and asynchronous failures; timing and bounce classification can depend on provider behavior. |
Scope, duration, and eligibility in this table describe the cited vendor documentation; they should not be copied as universal suppression rules. Check the policy for the sending service and account you actually use.
Keep bounce, complaint, and unsubscribe state separate
A delivery failure, a spam complaint, and an unsubscribe are different reasons to stop or limit mail. They may all affect whether you send, but one should not be recorded as another. Cloudflare documents complaints as a separate suppression reason, and M3AAWG treats opting out as a distinct list-owner action. Keep these states distinct so that a bounce event cannot erase an unsubscribe or mislabel a complaint.
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