TL;DR
- High Bounce Rate Auto Protection is off unless you turn it on when you set up a campaign.
- The rate is bounces divided by total leads in the campaign, not emails sent, so it starts low and catches problems late.
- Set a low threshold, and verify leads before import, since Smartlead can't verify a live campaign.
How the formula undercounts
Smartlead's help center gives the auto-protection formula as (bounces + latest bounce) / total leads × 100
(source).
Take a campaign with 2,000 leads. After the first 200 emails, 16 have bounced. That's an 8% real bounce rate on what you've sent. Smartlead's formula reads it as 16 ÷ 2,000 = 0.8%. A 3% threshold won't trigger until 60 bounces.
What threshold should you use?
Smartlead's own data puts the median cold email bounce rate at about 1.5%, with under 2% considered healthy (Smartlead blog). Its help examples use 3% and 5%. Because of the formula above, the lower end is safer for large campaigns.
Prevention beats protection
Smartlead only verifies at CSV import, and it sends to catch-all leads by default. Verify and split your list first. See how to verify leads for Smartlead.