What is the best practice for determining how many soft bounces before suppressing a user?
Michael Ko
Co-founder & CEO, Suped
Published 10 Jun 2025
Updated 17 Aug 2025
5 min read
Navigating the complexities of email deliverability often brings us to the topic of bounces, especially soft bounces. These temporary delivery failures, unlike hard bounces which indicate a permanent problem, can be tricky. They signal that an email couldn't be delivered on the first attempt, but there's a chance it could succeed later.
The challenge lies in deciding when a soft bounce transitions from a temporary hiccup to a persistent issue. Continuing to send emails to an address that consistently soft bounces can negatively affect your sender reputation and overall deliverability. It's a delicate balance, as you don't want to prematurely remove a valuable subscriber, but you also need to protect your sender score.
So, what's the best practice for determining how many soft bounces before suppressing a user? There isn't a single, universally agreed-upon number, as the optimal threshold depends on various factors specific to your email program.
Understanding soft bounces
Soft bounces occur for several reasons, indicating that the recipient's mail server temporarily rejected the email. Unlike hard bounces, which signify a permanent delivery failure (e.g., invalid email address), soft bounces are often remediable. Common reasons include a full mailbox, the recipient's server being temporarily down or overloaded, or the email message being too large.
Most email service providers (ESPs) attempt to resend soft-bounced emails multiple times over a certain period. The number of retries and the duration vary by ESP. For instance, some platforms will retry for up to 72 hours before classifying a persistent soft bounce as a permanent failure. It's important to understand how your specific ESP handles these bounce codes and soft bounce tolerance.
While 4xx SMTP codes typically indicate soft bounces (temporary failures), it's worth noting that some ESPs might eventually present these as permanent failures if retries are exhausted. This conversion means that by the time you see a 'soft bounce' in your analytics, it may have already become a hard failure from the ESP's perspective, especially if their internal queues have given up trying to deliver. This is why just relying on the 'soft bounce' label can be misleading sometimes.
Setting the threshold
There's no industry-wide consensus on the exact number of soft bounces before suppression. Different ESPs and email marketers adopt various thresholds based on their risk tolerance and sending patterns. For example, I've seen recommendations ranging from 3 to 7 consecutive soft bounces before an address is flagged for suppression.
Some platforms, like Klaviyo, might suppress after 7 consecutive soft bounces. Other providers, such as Mailgun, focus on overall bounce rate (aiming for 2-5%) rather than a strict soft bounce count. This variability highlights that a reasonable soft bounce tolerance is more of a strategic decision than a fixed rule.
ESP/Platform
Typical Soft Bounce Suppression Threshold
Mailchimp
7 to 15 consecutive soft bounces (converted to hard bounce)
Klaviyo
7 consecutive soft bounces
Salesforce Marketing Cloud
5 soft bounces, or 3 soft/hard bounces in 15 days
Brevo (formerly Sendinblue)
4 soft bounces
Iterable
Recommends 60-90 day window for bounce threshold
ATDATA
Recommends 6 consecutive soft bounces
Impact on deliverability and reputation
Your decision on soft bounce suppression should be influenced by several factors that directly impact your email deliverability and sender reputation (or lack thereof). A good domain reputation is crucial for reaching the inbox.
Aggressive suppression
Benefit: Quicker removal of problematic addresses, reducing the risk of being listed on a blacklist (or blocklist).
Drawback: Potentially losing genuinely engaged subscribers whose mailboxes were only temporarily full or servers briefly down.
Best for: Senders with high sending frequency (e.g., daily campaigns) where prolonged bounces quickly accumulate.
Conservative suppression
Benefit: Maximizes subscriber retention by giving addresses more time to recover from temporary issues.
Drawback: Higher risk of accumulating bad data and potentially impacting sender reputation if the soft bounces never resolve.
Best for: Senders with lower sending frequency (e.g., weekly or monthly newsletters) where temporary issues might resolve before the next send.
Engagement is also a key factor. If a user is consistently soft bouncing but also shows strong engagement signals (e.g., website visits, prior purchases), you might consider a slightly more conservative approach. However, if they're soft bouncing and showing no other signs of engagement, a more aggressive suppression strategy is probably warranted.
Practical considerations for your strategy
Given the variations, I suggest a strategy that balances risk mitigation with audience retention. Here’s how I would approach it:
Monitor soft bounce reasons: Understand if the bounces are consistently due to the same issue, like a full mailbox versus a server timeout.
Set a time-based threshold: Instead of just a count, consider a period, such as suppressing after 3-5 soft bounces within a 30-day window. This accounts for sending frequency.
Segment your soft bounces: Create a segment of users who have soft bounced. You can then exclude this segment from certain campaigns or try to re-engage them with different content or at different times.
Regular list cleaning: Routinely review and clean your email lists, particularly for inactive or consistently bouncing addresses.
Ultimately, the best strategy is proactive list hygiene and continuous monitoring. Don't wait until you're on a blocklist to address soft bounces.
Maintaining a healthy sender reputation
While there isn't a hard and fast rule, a good starting point for soft bounce suppression is around 3-5 consecutive bounces within a reasonable timeframe (e.g., 30-90 days), adjusting based on your sending frequency and audience behavior.
Prioritizing engaged users and maintaining a clean list will always yield better deliverability results than chasing inflated list sizes. Remember, a smaller, highly engaged list is far more valuable than a large list plagued by bounces and low engagement.
By actively managing soft bounces, you can improve your sender reputation, avoid email blacklists (or blocklists), and ensure your messages reach their intended recipients.
Views from the trenches
Best practices
Actively monitor soft bounce types and reasons to tailor your suppression rules.
Consider a suppression threshold of 3-5 consecutive soft bounces within a 30-day period.
Implement double opt-in to ensure new subscribers are genuinely interested and reachable.
Common pitfalls
Failing to define a clear soft bounce suppression policy, leading to reputation issues.
Treating all soft bounces the same, regardless of the underlying reason or frequency.
Prioritizing large list sizes over list hygiene and engaged subscribers.
Expert tips
If sending daily, 7 soft bounces in a quick succession is a reasonable threshold.
Analyze historical data to see how many soft bounces typically resolve for your audience.
Look at the specific SMTP codes returned, as some 4xx errors effectively act as hard bounces after retries.
Expert view
Expert from Email Geeks says a soft bounce is a rejection or deferral that will likely resolve itself.
2024-10-28 - Email Geeks
Expert view
Expert from Email Geeks says if you send too many emails before a soft bounce fixes itself and then suppress the address, you might remove a regular, deliverable recipient from your mailing list, which product teams often resist.
Mailchimp
Klaviyo
Salesforce Marketing Cloud
Brevo (formerly Sendinblue)
Iterable
ATDATA
