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A bounce handler should act on the recipient that failed, as identified in the delivery event—not the address that received the bounce, the visible From address, or the SMTP envelope sender. Those addresses have different jobs. Match the bounce to the original send, inspect the failed-recipient details, and suppress only when the failure warrants it.
Why a bounce can point to the wrong address
SMTP separates the message recipient from the destination for delivery-failure reports. The SMTP reverse-path tells receiving systems where to send those reports; on final delivery, it is represented by the Return-Path header. RFC 5321 describes its purpose as designating the address to which non-delivery or other mail-system failure messages are sent: RFC 5321, section 4.4.
That destination can be a dedicated error-handling mailbox or service. It is not necessarily the original recipient, and it is not necessarily the visible sender. If a handler suppresses the return-path address or the message’s From address instead of the failed recipient, it can leave the undeliverable address eligible for future sends while suppressing an unrelated address.
Which address should the handler suppress?
Use the recipient identified in the provider’s structured bounce event, correlated with the original send. For example, Amazon SES documents a bouncedRecipients list whose entries include the recipient emailAddress, action, status, and diagnosticCode. The bounce object also classifies the outcome as Permanent, Transient, or Undetermined: Amazon SES notification contents.
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Keep these identities separate in your data model:
- Visible sender: the message’s
Fromheader. - Return-path: the SMTP reverse-path used to route delivery-failure reports.
- Original recipient: the address your system tried to deliver to.
- Failed recipient: the recipient named by the bounce event; this is the address to evaluate for delivery suppression.
Store the provider’s event or message identifier alongside the failed recipient and the diagnostic details. This gives delayed notifications enough context to update the correct recipient rather than relying on message headers or a generic “bounce received” flag.
Classify the failure before suppressing
A bounce does not automatically prove that the recipient address is invalid. A permanent rejection identifying a nonexistent mailbox is a strong reason to stop sending to that recipient. A temporary failure may clear on retry. A rejection related to policy, content, authentication, or sender reputation may require a sending-configuration fix rather than recipient suppression.
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Use the full diagnostic response as well as the provider’s category. M3AAWG notes that numeric codes and explanatory text are not uniform across receiving systems; its guidance distinguishes address problems from temporary and policy or reputation failures: M3AAWG Recommendations for Senders Handling of Complaints. Salesforce likewise cautions that providers do not follow one universal standard and that temporary DNS or network problems can resemble a permanent address problem: Salesforce Help: Enable Email Bounce Handling.
- Permanent invalid recipient: suppress that recipient according to your sending policy.
- Temporary or transient failure: retain the diagnostic and retry only under an appropriate retry policy; do not assume the address is bad.
- Policy, content, authentication, or reputation rejection: investigate the sending setup or message. Suppressing a valid recipient does not resolve a sender-side problem.
- Undetermined or ambiguous result: preserve the event for review or cautious handling rather than treating a label alone as proof of an invalid address.
Handle delayed bounces and retries safely
Some receiving systems accept a message first and report a delivery failure later. The notification may arrive after the send request has completed, so a handler that processes only immediate send responses can miss it. Salesforce documents both in-band and asynchronous failures, and M3AAWG discusses delayed failure notifications.
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Build the event path around the original send and the specific failed recipient. Record the event time, recipient, bounce type or subtype, SMTP status, diagnostic text, and provider identifiers when available. Make processing idempotent—replaying the same event should not create conflicting records or suppress different recipients—and apply the resulting status only to the matched recipient. The precise idempotency mechanism is an implementation choice, not an SMTP rule.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Suppression scope and duration depend on the provider
SMTP does not prescribe a universal suppression list, scope, or expiry period. Provider policies can differ substantially:
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| Provider example | Recipient and classification details | Suppression scope or duration |
|---|---|---|
| Amazon SES | The bounce notification includes a recipient list with address, action, status, and diagnostic code; bounce type is classified as permanent, transient, or undetermined. SES advises removing recipients after permanent bounces, while transient failures may permit later sends and are retried for a period. | Not stated in the cited notification documentation; see Amazon SES notification contents. |
| Cloudflare Email Service | Distinguishes recipient suppression from sender-side authentication or reputation failures, which do not create recipient suppressions. | Documents account-level and sending-domain scopes. Eligible soft-bounce suppressions default to 24 hours; eligible permanent-rejection suppressions may expire after seven days or have no expiry, depending on the reason. These are Cloudflare policies, not SMTP rules: Cloudflare suppression lists. |
| Azure Communication Services | Uses a managed suppression list for specified hard-bounce codes. | The managed suppression lease can extend after repeated invalid-recipient sends and has a documented maximum of 14 days. This is Azure-specific behavior: Azure Communication Services managed suppression list. |
| Salesforce | Processes delivery status notifications into contact, lead, or person-account status and marks a record bounced only for hard bounces. | Not stated in the cited guidance: Salesforce Help: Enable Email Bounce Handling. |
Do not treat a provider’s “hard bounce” label, suppression duration, or list scope as a universal protocol requirement. Preserve the underlying evidence and apply the policy that fits the failure and your system.
Keep delivery failures separate from complaints and opt-outs
A delivery failure, a complaint, and an unsubscribe are different events with different meanings. Cloudflare documents complaints as a separate suppression reason, and M3AAWG treats opt-out as a separate list-owner action. Keep these states distinct so that a bounce handler does not accidentally overwrite consent or complaint records—or treat an unsubscribe as a failed delivery.
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