Hard-bounce suppression stops sends to an address. A hard bounce means the recipient server considers the address permanently undeliverable.1 A bounce applies to a specific recipient.2 The suppression may need to cover every sending category. When a hard_bounce suppression applies to all, it blocks both marketing and transactional messages.3 Run each event through classification, suppression, scope review, and controlled removal.
Run the workflow
Follow the stages in order. First identify the failure. Last, decide whether a later change supports removing protection.
| Stage | What you are trying to learn | Example question |
|---|---|---|
| Classify | Whether the delivery failure supports permanent suppression | What did the recipient server report? |
| Suppress | Whether the address is blocked before another send | Has this address entered the suppression list? |
| Check scope | Which message categories the block covers | Does the suppression apply to every relevant send? |
| Review removal | Whether a verified change supports removing the block | What changed since the hard bounce? |
Classify the bounce
Start with the delivery failure. Campaign performance does not show whether one address is permanently undeliverable.
A bounce message usually includes a failure code and a description of the cause.4 Read both before assigning the event to a suppression rule. Invalid-mailbox and invalid-domain are recognized as hard-bounce categories.5 An inactive-mailbox response can mean that the address is disabled, abandoned, or no longer exists on the recipient server.6 Check how your sending system classifies that response before applying a permanent block.
Only a bounce classified as hard should trigger address suppression.7 Keep the original response with the record so a later review can distinguish a corrected address from one that remains undeliverable.
Add the address to suppression
After confirming that the event is hard, stop the address before the next campaign or message is assembled. The suppression record prevents an accidental retry.
Hard bounces should be added to the suppression list immediately.8 Most reputable email service and marketing automation providers automatically suppress hard bounces.9 Verify that the event created a suppression record instead of assuming the automation worked. Check the address against the next audience before sending.
An account-level suppression list contains hard bounces only.10 When this list is used, the same addresses can also be added to a global suppression list.11 This distinction matters when you operate more than one sending stream. Check both the local rule and any wider block before declaring the address handled.
Check suppression scope
The block must reach every message type that could otherwise send to the address. Review the scope after the record exists. An address can appear suppressed in one workflow while remaining eligible in another.
Check whether the rule applies to all categories, marketing messages, transactional messages, or a narrower segment. With hard_bounce and applies_to: all, the suppression blocks both marketing and transactional messages.3 Keep the address as the unit of action. A single-recipient failure does not require a campaign-wide pause.
Review removal
Removal needs a reason you can verify. Before changing the record, check whether the address was corrected, whether the recipient confirmed a replacement, and whether the sending path changed.
If a one-off email to the corrected address still bounces, the address should remain suppressed.12 Keep the old address blocked and handle the replacement as a separate address. Record what changed and why removal is safe, then test the new state with the smallest possible send permitted by your workflow.
Prevent recurrence
Suppression contains the immediate problem. Use the review to reduce the chance that future sends create more invalid addresses or repeat the same delivery failure.
Authenticate the email domain and configure DMARC to help prevent bounced emails.13 If the From address uses a free email service, switch to an address from a private domain.14 Remove or suppress unengaged profiles to reduce future invalid-address bounces.15 Apply these controls before expanding a list. Suppression handles the failed address after the event, while list and domain practices reduce the number of failures entering the workflow.
What not to do
These mistakes can turn a single delivery failure into a repeat event or make a later review harder.
- Do not keep sending to a hard-bouncing address. Repeated attempts can damage sender reputation or lead to blocking by the recipient server.16
- Do not remove a hard-bounce record casually. An address that still does not exist will bounce on the next send and be suppressed again.17
- Do not submit a removal request without describing the measures taken to prevent the same bounces, when those measures apply.18