What Is a Bounce?
An email "bounce" occurs when a message you send cannot be delivered to the recipient's inbox. Bounces are one of the most critical metrics in cold email - high bounce rates affect your sender reputation faster than almost anything else.
Types of Bounces
Hard Bounces
The email address is permanently undeliverable. Common causes:
The email address does not exist
The domain does not exist
The recipient's mail server has permanently rejected your message
Hard bounces are the most damaging. Even a small percentage tells email providers you are sending to unverified or purchased lists.
Soft Bounces
The email address exists but the message could not be delivered temporarily. Common causes:
Recipient's mailbox is full
Recipient's mail server is temporarily unavailable
Message is too large
In rare cases, a temporary block from the receiving server
Soft bounces are less severe, but repeated soft bounces to the same address can eventually count against you.
What Bounce Rate Should You Aim For?
Bounce Rate | Status | Action |
Under 2% | Healthy | No action needed. Keep doing what you are doing. |
2%–5% | Caution | Review your lead list quality. Re-verify before sending more. |
Over 5% | Critical | Pause sending immediately. Clean your list and review the cause. |
Industry standard for cold email: Keep your bounce rate below 2% at all times.
How Prospi's Auto-Pause Works
Prospi continuously monitors your campaign bounce rates in real time. When your bounce rate exceeds a safe threshold, Prospi automatically pauses the campaign to protect your sender reputation.
What Happens When a Campaign Is Auto-Paused
Sending stops immediately - No more emails go out from the affected campaign.
You receive a notification - Prospi alerts you that the campaign has been paused and shows the bounce rate.
Other campaigns are unaffected - Auto-pause is per-campaign, so your other campaigns continue running normally.
Warmup continues - Your email warmup is not interrupted, keeping your account reputation stable.
Why Auto-Pause Matters
Without auto-pause, a low-quality lead list could send hundreds of emails to invalid addresses before you notice - potentially affecting your domain reputation or getting your email account suspended. Prospi's auto-pause acts as a safety net, catching elevated bounce rates before they cause lasting impact.
What to Do When a Campaign Is Paused
Step 1: Identify the Cause
Check the bounced email addresses in your campaign report. Look for patterns:
All bounces from one domain? That company's mail server may be blocking you or the domain may be defunct.
Random bounces across many domains? Your lead list likely contains unverified or outdated data.
Soft bounces only? This may be a temporary situation. Wait and try again.
Step 2: Clean Your List
Remove all hard-bounced addresses permanently
Re-verify remaining leads using Prospi's built-in email verification (powered by Prospi's verification system + catchall detection)
If you imported leads from an external source, consider switching to Prospi's double-verified lead database
Step 3: Resume the Campaign
Once you have cleaned the list and are confident in data quality, resume the campaign from Prospi's dashboard
Monitor bounce rates closely for the first 24–48 hours after resuming
If the campaign pauses again, do not force-resume - review further
How to Prevent High Bounce Rates
Use Verified Data
Always verify before sending - Use Prospi's built-in verification on every list, even if the data came from a "verified" source.
Use Prospi's lead database - Leads are double-verified, significantly reducing bounce risk.
Be cautious with catchall domains - Catchall domains accept all emails, so addresses cannot be verified. Prospi's catchall detection flags these so you can decide whether to include them.
Keep Lists Fresh
People change jobs and email addresses become invalid. A list verified 3 months ago may have changed significantly.
Re-verify any list that is more than 30 days old before using it in a new campaign.
Start Small
When testing a new lead source or list, send to a small batch first (50–100 contacts).
If bounce rates are healthy, scale up gradually.
This limits your exposure if the data turns out to be lower quality than expected.
Frequently Asked Questions
Can I adjust the auto-pause threshold?
Prospi's auto-pause thresholds are set to industry-safe levels to protect your accounts. We do not recommend overriding them, as the risk of reputation impact far outweighs the benefit of sending a few more emails.
Does a paused campaign affect my sender reputation?
The bounces that already occurred will have some impact, but auto-pause prevents further impact. The sooner a campaign is paused, the less effect on your reputation. This is why the feature exists - to catch things early.
What about "catch-all" bounces?
Catchall domains accept all incoming email, so verification tools cannot confirm whether a specific address exists. Prospi flags these leads separately. You can choose to include them (accepting slightly higher risk) or exclude them for maximum safety.