Bounce Rate Limits by Platform: When Each ESP Takes Action

Published bounce limits range from 2% to 10%, and many platforms publish none at all. Brevo can suspend above a 2% hard bounce rate, HubSpot at 5% in a month, Amazon SES reviews at 5% and may pause at 10%, and Postmark requires under 10%. Mailchimp and Mailgun enforce thresholds they do not disclose.

The table below is built only from each vendor's own help pages, read on 1 October 2026. Where a vendor says a threshold exists but gives no number, the table says "not published". We did not fill gaps with figures from third-party blogs, several of which quote numbers that the vendors' own pages do not contain.

If you want the background on why bounces happen in the first place, that is covered in why cold emails bounce. This post is only about where the lines are and how each platform counts.

The published thresholds, platform by platform

Most platforms publish either a hard enforcement line or a "healthy" benchmark, rarely both. The table separates the two, because a benchmark is advice and an enforcement line is what actually stops your sending.

Platform	Bounce line	What happens	Complaint line	Source
Brevo (marketing)	Hard bounce rate above 2%	Campaigns or account can be suspended	Above 0.2% (unsubscribes above 1%)	Brevo help
HubSpot (marketing email)	Hard bounce rate of 5% in a month	Account may be suspended	Spam reports 0.1% (unsubscribes 3%)	HubSpot KB
Amazon SES	5% = under review; 10% = may pause	Review period, then sending pause	0.1% = review; 0.5% = may pause	AWS SES FAQ
Postmark	Must stay below 10%	Sending suspended; ToS allows cancellation	Below 0.1%	Postmark FAQ, ToS
Instantly	5% by default (adjustable)	Campaign auto-paused after 200+ sends	Not published	Instantly help
lemlist	Alert at 10%; auto-pause at 50%	Campaign paused once 100+ leads contacted	Not published	lemlist help
Smartlead	You set it (no default stated)	Campaign paused, webhook fired	Not published	Smartlead help
SendGrid (Twilio)	Not published (advises checking if "consistently over 5%")	Account review states: warned, suspended, deactivated, banned	Not published (calls above 0.1% "excessive")	Twilio docs
Mailchimp (marketing)	Not published	Warning, then automatic suspension	Not published	Mailchimp help
Mailchimp Transactional	Not published (advises hard bounces below 5%)	Reputation and hourly quota fall	Not published (advises under 0.1%)	Mailchimp developer docs
Mailgun	Not published	Domain temporarily disabled	Not published	Mailgun help
Klaviyo	Not published (above 2% "needs attention")	Deliverability alerts	Not published (above 0.05% "needs attention")	Klaviyo help
Constant Contact	Not published	Address-level suspension (see below)	Not published	Constant Contact KB
Gmail / Google Workspace	Not published ("a large number")	Sending blocked for up to 24 hours	Spam rate below 0.3%, ideally 0.1%	Gmail limits, sender guidelines

Two things stand out. First, the published enforcement lines cluster at 2%, 5% and 10%, not around one industry number. You will often read that platforms "warn at 3%"; none of the pages we read publishes that figure. Second, the platforms with the largest volumes are the least specific. Mailchimp's help centre says outright that "ISPs do not publicly release their limits", and Mailgun says only that it "has thresholds in place".

The same campaign gives a different bounce rate on each platform

A bounce rate is a fraction, and platforms disagree about both the top and the bottom of it. Before you compare your number to any line in the table, check what your platform counts as a bounce and what it divides by.

What counts as a bounce. Amazon SES is the most explicit. Its bounce rate "includes only hard bounces to domains you haven't verified". Mailbox-full errors and bounces caused by a blocked IP do not count. HubSpot and Brevo both name the hard bounce rate. Instantly's and lemlist's help pages say "bounce rate" without spelling out whether soft bounces are included, so check your own campaign analytics before assuming.

What it is divided by. Smartlead's help centre publishes its formula: (total bounce count + latest bounce) / total_lead_count * 100. The denominator is the total number of leads in the campaign, not the number of emails sent so far. Instantly waits until at least 200 emails have gone out before checking, and lemlist waits until 100 leads have been contacted.

Over what period. HubSpot measures "in a specific month". Brevo looks at campaigns sent in the last 24 hours, and for a send to new contacts it assesses a random subset within one to three hours. Amazon SES uses neither. It looks at a "representative volume" that differs per account, and its FAQ says you cannot reproduce the figure exactly from the console or the GetSendStatistics API.

A worked example

Take one cold campaign: 5,000 leads loaded, the first 1,000 emails sent, 60 of them hard-bounced. Here is what each platform's published rules imply, applied by hand to those numbers:

Platform rule	Calculation	Result
Instantly, default 5%, checked after 200 sends	60 / 1,000 = 6.0%	Paused
Smartlead, threshold set to 5%, divides by total leads	60 / 5,000 = 1.2%	Keeps sending
lemlist, alert at 10%, pause at 50%	60 / 1,000 = 6.0%	No alert
Brevo, hard bounce line 2%	60 / 1,000 = 6.0%	Over the suspension line

Same 60 dead addresses, four different outcomes. The receiving mailbox providers, meanwhile, saw 60 attempts to deliver to mailboxes that do not exist out of 1,000 messages, whatever your tool reported. A safety net with a large denominator or a high trigger catches you late.

Account-level, domain-level and address-level enforcement

Platforms act at different levels, and the level tells you what you lose when you cross the line.

• Account level. HubSpot, Brevo, Amazon SES, Postmark and SendGrid act on the whole account. HubSpot adds that suspensions on accounts using only its free tools "cannot be lifted". Brevo warns that if an account is suspended a second time, "we won't be able to reactivate it".
• Domain level. Mailgun disables the sending domain temporarily and asks you to clean the list and contact support before it is re-enabled.
• Campaign level. Instantly, Smartlead and lemlist pause the campaign, not your mailboxes or account. That is a protective feature you can switch off, not an enforcement action by the platform.
• Address level. Constant Contact marks an address as "Suspended" once it has repeatedly bounced as non-existent across any Constant Contact account, and will not send to it again. Amazon SES keeps a global suppression list of addresses that recently hard-bounced for any SES customer. A send to one of those addresses still counts as a hard bounce against your rate, even though SES never attempts delivery.

That last point matters for imported lists. On SES, an address another customer has already burned can count against you on your first send to it.

Complaint lines are much tighter than bounce lines

Every published complaint threshold is an order of magnitude below the bounce thresholds: 0.1% at HubSpot, Postmark and SES review, 0.2% at Brevo. Gmail's own sender guidelines ask bulk senders to keep the spam rate in Postmaster Tools below 0.3% and ideally below 0.1%. See the Gmail and Yahoo bulk sender requirements for the full rules.

The two are connected. A list with enough dead addresses to push bounces over 2% is usually old or bought, and the live addresses on it belong to people who do not remember signing up. Those are the people who press "report spam".

What Gmail does with a personal or Workspace account

Gmail does not publish a bounce percentage for ordinary accounts, but it does act on bounces. Its help page on sending limits lists the error "Messages you sent couldn't be delivered" for when "a large number" of your emails go to invalid addresses or bounce. In that case you may be able to send again after 24 hours.

Google Workspace accounts have fixed sending limits: 2,000 messages a day, 10,000 total recipients and 3,000 external recipients, applied over a rolling 24 hours. Hitting them stops sending for up to 24 hours. That matters if you send cold email straight from Workspace inboxes, because on that path there is no ESP auto-pause to catch a bad list first.

How to use these numbers

Do not aim for the threshold; aim well under the strictest one that applies to you.

1. Find your platform's actual line in the table, then check its definition of bounce rate and its time window. If it is "not published", plan as if it were 2%, the lowest published line.
2. Measure the way the strictest receiver would: hard bounces divided by messages actually sent. Ignore a tool's figure if it divides by total leads.
3. Set your own auto-pause lower than the default. Instantly lets you change its 5% default and Smartlead requires you to choose one. A line at 2% gives you time to react before a platform or mailbox provider does.
4. Verify before the first send, not after the first pause. All of these thresholds measure damage after it has happened. A verification pass removes the non-existent mailboxes that make up most hard bounces before any of them count.
5. Treat repeat soft bounces separately. They mostly do not count toward hard bounce rates, but several platforms convert them to hard bounces after enough repeats. The rules are in handling soft bounces.

The useful conclusion from reading every one of these pages is that there is no single safe number. Lines run from 2% at Brevo to 10% at Postmark, and the platforms that publish nothing can act at any point. A list that bounces under 2%, measured honestly against messages sent, stays under every published line in the table.