What is Bounce Rate (Email)?
Definition: The percentage of sent emails that fail to deliver, either because the address does not exist (hard bounce) or the mailbox is temporarily unavailable (soft bounce).
Bounce rate is the single most important metric for cold email deliverability. Keep it under 2%. Above 3%, email providers start flagging your sending domain. Above 5%, you're heading toward blacklists.
Hard bounces mean the email address doesn't exist. The person left the company, the domain expired, or the enrichment data was wrong. These are permanent failures. Soft bounces mean the mailbox exists but can't receive mail right now: full inbox, server down, or message too large. Soft bounces are temporary and usually resolve themselves.
GTM Engineers control bounce rate through two mechanisms: verification before sending (run every list through NeverBounce or a similar service) and list hygiene over time (remove addresses that bounce on first send, suppress known bad domains). Some sequencing tools like Instantly handle verification automatically, but it's safer to verify independently.
Watch for catch-all domains. These accept all emails regardless of whether the specific address exists. A catch-all domain will pass verification but still bounce in practice because the actual mailbox doesn't exist. FullEnrich and Clay flag catch-all domains so you can handle them separately, usually by sending to them in smaller batches and monitoring results.