What is the best practice for determining how many soft bounces before suppressing a user?
Updated on 10 Oct 2026: We updated our soft bounce suppression advice with cadence-based time windows, temporary suppression, and recipient-level failure checks.
A practical starting range for a custom suppression policy is 3 to 7 consecutive soft bounces, measured across enough calendar time to establish persistent delivery failure. Start with 5 consecutive soft bounces over at least 14 days, then tune the rule using recovery data and your sending platform's controls. For engaged recipients in daily or more frequent programs, 7 consecutive failures over at least 14 days is an option to test. For weekly sends, 3 failures span about 14 to 21 days; for monthly sends, allow about 60 to 90 days.
The number alone is the wrong control. Five soft bounces in one afternoon can be a provider incident or throttling event. Five soft bounces across 5 weeks points to a mailbox that is not accepting your mail consistently.
- Start with 5 consecutive recipient-level soft bounces across at least 14 days for a custom marketing policy.
- Consider 7 consecutive failures over at least 14 days for engaged recipients in high-frequency programs.
- For 3 consecutive failures, use about 14 to 21 days for weekly sends and 60 to 90 days for monthly sends.
- Use a lower threshold for dormant recipients with persistent mailbox failures; investigate widespread bounce spikes before suppressing addresses.
Why soft bounce thresholds vary
A soft bounce is usually treated as a temporary delivery failure, but email service providers (ESPs) do not use one universal definition. One platform can label a full mailbox as a soft bounce, another can include a temporary domain failure, a third can include a remote server timeout, and a fourth can show a 4xx deferral only after retries have already expired. Some platforms also classify certain 5xx mailbox rejections as soft bounces when they believe the failure is not permanent.
A bare setting such as "suppress after 5 soft bounces" is unreliable unless you know exactly what the platform means by soft bounce. If the bucket includes deferrals, mailbox-full responses, temporary suspension messages, DNS lookup trouble, remote server timeouts, and generic policy blocks, a single threshold can suppress people for reasons that have nothing to do with their mailbox validity. A Reddit discussion of soft bounce handling describes different thresholds and recovery rules used by practitioners.
Do not suppress on count alone
A soft bounce count has to be paired with elapsed time, SMTP response patterns, engagement, and current sending health. Otherwise, one temporary provider incident can push good subscribers into suppression.
The safest way to set the threshold is to look at your own recovery curve. Export users who soft bounced, then measure how many later received successfully and how many never recovered. Define recovery as a subsequent successful delivery to the same address, and compare recovery after each failure count by bounce reason and sending cadence. If someone has failed across several campaigns and enough calendar time has passed, continued sending usually adds reputation risk without much upside.
Suped's DMARC and email authentication platform helps investigate sender-level problems through DMARC monitoring, SPF and DKIM checks, and alerts. Combine that evidence with your sending platform's bounce logs when deciding which addresses to suppress. If soft bounces jump because authentication broke or a sending domain is listed on a blacklist (blocklist), investigate the sending issue first.
Soft bounce suppression flowchart checking bounce reason, consecutive failures, elapsed days, and engagement.
A suppression rule that works in practice
A practical setup without dedicated marketing operations staff should balance deliverability risk with the chance that a temporarily unreachable recipient comes back. The rule has four parts: consecutive failures, elapsed days, bounce reason, and engagement status. These are custom-policy examples; respect the platform's existing automatic suppression rules.
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Multiple daily | 7 over at least 14 days | Fast senders can hit 3 failures before a mailbox owner has time to fix quota. |
Daily | 5-7 over at least 14 days | Enough attempts to catch temporary issues without mailing indefinitely. |
Weekly | 3 over 14-21 days | Three weekly failures span about 14 days when measured between the first and third failed sends. |
Monthly | 3 over 60-90 days | A higher count would keep bad addresses active for too long. |
Triggered only | 3 with manual review | Transactional context matters, so review before global suppression. |
Suggested custom thresholds for consecutive recipient-level soft bounces
The most important wording is "consecutive." If a user soft bounces twice, then receives successfully, the counter should reset. Use a delivered event that records receiving-server acceptance to identify recovery. A submitted or queued event does not establish delivery, and server acceptance does not prove inbox placement. Suppressing later based on lifetime soft bounces can punish old temporary failures that no longer matter.
Simple suppression logictext
if confirmed_permanent_recipient_failure: suppress_address_for_all_email stop_processing if sender_or_message_failure: investigate_sender_or_message stop_processing if final_delivery_result == successful_delivery: reset_consecutive_counter if final_delivery_result == recipient_soft_bounce: increment_consecutive_counter_once_per_recipient_message if consecutive_soft_bounces >= threshold and days_since_first_soft_bounce >= minimum_days: suppress_from_marketing_for_cooldown if user_requests_transactional_message: apply_transactional_policy_and_existing_suppressions
Suppress promotional and lifecycle marketing first when the platform supports separate policies. Password resets, security alerts, receipts, and account messages need a separate policy that respects permanent recipient failures and existing platform suppressions. For manual reactivation of lasting bounce suppression, verify an updated address or obtain evidence that the existing address has recovered. Record the reactivation source and retain the original suppression reason and date.
If your platform only offers a blunt soft bounce filter, set it conservatively and monitor the effect for a few sends. Compare suppressed users against verified clicks, purchases, logins, or other recent activity. Opens alone are unreliable because automated image loading can inflate them. A recently active customer with 3 soft bounces deserves more caution than a dormant subscriber who has not engaged in 18 months.
Use temporary suppression before permanent suppression
A temporary suppression period gives a recoverable mailbox time to clear without further marketing sends. For mailbox-full failures, a 14-day cooldown is an example to test, separate from the minimum elapsed-time rule used to trigger suppression. Follow the platform's existing suppression behavior when it applies.
- Pause marketing sends during the cooldown while retaining the bounce reason and delivery history.
- After the cooldown, review sender health, consent, and recent customer activity before allowing a recovery trial.
- If the address remains eligible, allow one current, consented message at the normal cadence. Reset the consecutive counter after successful delivery.
- Keep the address suppressed if the recovery trial fails. Review permanent marketing suppression after repeated failed cooldown cycles.
Store the email address, SMTP reason, cooldown expiry, and failed-cycle count in the suppression list. Preserve this history across imports and duplicate profiles so recreating a contact does not restart sending. Suppression stops sending without deleting the customer record.
Count failed messages, not retry attempts
A receiving server can issue multiple temporary 4xx responses while one message remains queued. Those retry attempts belong to one queued message and should not advance a recipient's consecutive soft bounce counter several times. For a custom recipient counter, count the final failed message after the sending platform exhausts its retries. Confirm native ESP counting rules separately, since built-in suppression can count errors differently.
- Count at most one soft bounce per recipient and message, only if delivery ultimately fails.
- Increment when a separate message ends in a final recipient-level soft bounce.
- Reset the consecutive counter when a subsequent message is delivered successfully to the same address.
- Confirm whether the event means a deferral, an automatic retry, a temporary failure report, or a final failure before automating suppression.
This distinction prevents a short receiving-server incident from looking like repeated campaign-level failure. It also makes recovery-rate analysis comparable across sending platforms with different retry schedules. Deduplicate repeated bounce webhooks by recipient and message ID. Apply delayed non-delivery reports (NDRs) to the original message and evaluate outcomes in send order.
Separate true mailbox problems from sender problems
Before suppressing users based on soft bounces, check whether the failures are clustered by recipient domain, sending IP, sending domain, campaign, or authentication result. If one campaign suddenly soft bounces at a major mailbox provider more than usual, the problem is not necessarily the individual subscribers.
Mailbox-level signal
- The same recipient soft bounces across different sends and dates.
- Mailbox full, temporary mailbox disablement, or other recipient-specific acceptance trouble can cause this pattern.
- Suppress after the threshold and keep a reactivation path.
Sender-level signal
- Many recipients at one domain fail at the same time.
- Common causes include throttling, weak reputation, authentication failures, DNS trouble, or a blocklist or blacklist issue.
- Pause automated recipient suppression for clustered sender failures and fix the sending problem first.
This distinction matters because a soft bounce can be a deliverability symptom. A temporary suspension response, a DNS failure, a missing DKIM signature, or a sudden blacklist (blocklist) event can create soft bounce noise that has nothing to do with the user's address quality.
Email tester
Send a real email to this address. Suped shows a results button when the test is ready.
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When soft bounces spike, send a real message through the same stream and inspect the result with Suped's email tester. It checks authentication and sending setup on the received test message. Use the original bounce logs to investigate recipient-specific rejection reasons before changing suppression rules.
For domain-level checks, Suped's domain health checker is useful when bounce behavior looks broader than one campaign or one recipient. It lets you verify DMARC plus SPF and DKIM posture before you decide the list itself is the main problem.
What to do with different soft bounce reasons
The best suppression policy treats soft bounce reasons differently when your platform exposes them. If the platform only provides a general soft bounce bucket, you can still use domain clustering, send timing, campaign context, and raw SMTP text when available.
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Mailbox full | Often recoverable | Use the cadence-based threshold or a temporary suppression period; review recovery for engaged recipients. |
Temporary deferral | Can be throttling | Check domain-level clustering before suppressing. |
Domain unreachable | Temporary DNS or remote server outage, or an invalid destination domain | Investigate DNS and domain-wide patterns. Suppress immediately only when the recipient domain is confirmed invalid. |
Policy block | Sender or message policy issue | Investigate authentication, reputation, content, and sending patterns before suppressing. |
Disabled mailbox | Temporary or permanent; inspect the enhanced status code and diagnostic text | Review 4.2.1 versus 5.2.1 and the stated cause before choosing a cooldown or permanent suppression. |
Message too large | Message or attachment exceeds the receiver's size limit | Reduce message size; a size rejection does not establish that the address is invalid. |
5.1.1, mailbox does not exist | Permanent recipient failure | Suppress the address immediately instead of waiting for the soft bounce threshold. |
How to interpret common soft bounce reasons
A temporary deferral is especially tricky. In many platforms, the sender does not see every 4xx retry event. The platform retries behind the scenes, then reports a final failure only after the message leaves the queue. By the time you see the soft bounce, that individual message has permanently failed, even though the SMTP response class looked temporary.
A raw response can change the decision
Example SMTP responsetext
451 4.3.0 [internal] Sending IP temporarily suspended
This kind of response points to a sender-side or platform-side condition. Suppressing individual subscribers because of it would hide the real issue.
When the status code and diagnostic text point in different directions, use the full response and delivery history instead of mapping every 4xx response to keep and every 5xx response to suppress. RFC 5321 defines 4xx as transient failures and 5xx as permanent rejections of the SMTP request. A 5xx sender-policy or message-size rejection does not establish that the recipient address is invalid; correct the cause before reviewing a resend.
A measured rollout plan
Roll out suppression changes in stages instead of turning on a new rule globally without evidence. The goal is to prove the rule reduces repeated failed delivery without removing recently active people who were likely to recover.
Illustrative custom suppression thresholds
Apply recipient-level reason checks and the cadence-specific time window; these ranges do not replace platform rules.
Observe
1-2 soft bounces
Investigate the reason and any domain-wide spike before assuming a mailbox problem.
Review
3-4 soft bounces
Check reason, domain clustering, and engagement.
Suppress
5-7 soft bounces
A suggested custom trigger when recipient-level failures are consecutive and meet the time window.
Start by tagging affected users instead of suppressing them. Run the tag for 2 to 4 weeks for daily or weekly sends, or 60 to 90 days for monthly sends. Keep the normal sending cadence and respect existing suppressions. Continue sending only to a consented, controlled sample, then check how many tagged users later receive successfully, how many engage, and how many continue to fail. If very few users recover after the third or fifth failure, the suppression rule is justified.
- Measure soft bounce rate as final soft-bounced messages divided by attempted messages, multiplied by 100, alongside hard bounce rate, complaints, and delivered volume.
- Mark users after the proposed threshold, but keep only a controlled sample eligible during the test window.
- Look at recovery rate, recent engagement, revenue, and failure clustering.
- Suppress users who match the rule after the test supports it.
- Recheck the rule after seasonality, send volume, audience mix, or platform behavior changes.
Issues page showing top issues, verified sources, unverified sources, and authentication pass rates
Suped's issue view is useful when suppression changes coincide with authentication or sender-source issues. It gives a clear view of verified and unverified sources, authentication pass rates, and the specific fixes needed, so the list hygiene work does not mask a broken sender setup.
When to use a lower suppression threshold
A 5-over-14-days starting rule is practical, but some cases justify a tighter threshold. Soft bounces are not always dangerous. Tighten the threshold when surrounding signals show that sender reputation or audience quality is already under pressure.
- For dormant recipients with persistent mailbox failures, test 3 to 5 failures with an elapsed-time rule.
- Suppress confirmed nonexistent mailboxes immediately instead of waiting for repeated soft bounces.
- Reduce sending to weak segments and fix consent or targeting issues.
- Check domain and IP reputation before deciding the bounce problem is subscriber-level.
When reputation is already fragile, reduce sending to dormant recipients with persistent mailbox failures. A threshold of 3 consecutive recipient-level soft bounces across at least 15 days is a candidate to test for these recipients. Authentication failures, domain-wide throttling, and sender policy blocks require investigation before recipient suppression.
Use Suped's blocklist monitoring to investigate reputation-related bounce increases. A blocklist (blacklist) listing is sender-level evidence and should prompt investigation before recipient suppression.
Suggested custom starting policy
Start with 5 consecutive recipient-level soft bounces over at least 14 days for a custom marketing policy. Reset the counter after successful delivery. Test 3 for dormant recipients with persistent mailbox failures, and 7 for engaged high-frequency recipients. Apply the elapsed-time rule and respect native platform suppressions.
Views from the trenches
Best practices
Pair soft bounce counts with elapsed days so one short outage cannot suppress valid users.
Reset the soft bounce counter after successful delivery to avoid punishing old failures.
Review domain clustering before suppression, since sender issues can look like list decay.
Common pitfalls
Treating all platform soft bounce labels as equal creates bad suppression decisions.
Using lifetime soft bounce totals keeps stale failures attached to healthy recipients.
Ignoring send cadence makes daily and monthly programs follow the same bad threshold.
Expert tips
Start with five consecutive soft bounces over fourteen days, then tune with recovery data.
Use three failures for dormant users where recovery value is low and reputation risk is high.
Check raw SMTP text when available because some soft bounces point to sender-side issues.
Expert view
Expert from Email Geeks says a configurable soft bounce threshold needs nuance, because some platforms convert repeated soft bounces into harder suppression states only after multiple consecutive failures.
2024-10-28 - Email Geeks
Marketer view
Marketer from Email Geeks says seven consecutive failures can be too slow for some programs, and the better approach is to inspect how many recipients recover after the first few attempts.
2024-10-28 - Email Geeks
Recommended soft bounce suppression rule
A custom marketing policy can start with 5 consecutive soft bounces over at least 14 days, reset the count after successful delivery, and adjust the threshold by send frequency and engagement. Test 3 for dormant recipients with persistent mailbox failures and 7 for engaged high-frequency recipients, retaining the applicable elapsed-time requirement. Do not use lifetime soft bounce totals or automatic SMTP retry events as the suppression trigger.
Before turning the rule on, check whether recent soft bounces are concentrated by recipient domain, sending source, campaign, or raw SMTP reason. If the pattern points to authentication, DNS, policy blocks, or a blacklist (blocklist) event, fix the sending issue first. Suped's DMARC reports and SPF/DKIM visibility support authentication diagnosis; keep recipient-level bounce counters in your sending platform.
