Email bounce rate
Email bounce rate is the percentage of sent emails that are returned undelivered. Hard bounces are permanent (invalid or non-existent address); soft bounces are temporary (full mailbox, server down). A high bounce rate signals a poor list and damages sender reputation.
How it works
When a mail server can't deliver a message it returns a bounce code. Hard bounces should be suppressed immediately; repeated sends to invalid addresses tell providers you don't maintain your list.
Why it matters
Bounce rate is a direct deliverability signal. Most providers want cold-outreach bounce rates well under ~3-5%; above that, placement drops and accounts get flagged.
How Autocloz handles it
Autocloz verifies addresses before sending, auto-suppresses hard bounces, and surfaces bounce trends per mailbox so a bad list segment can't silently burn your domain.
FAQ
What is a good email bounce rate?
For cold outreach, keep hard bounces under about 3%. The reliable way to get there is verifying every address before the first send and suppressing bounces automatically.
Related terms
A spam trap is an email address operated by mailbox providers and blocklist operators specifically to catch senders with poor list hygiene. There's no real person behind it, so any mail it receives indicates you're emailing addresses you didn't earn permission to contact.
Email verification is the process of checking whether an email address is valid and safe to send to — confirming the syntax, domain and mailbox exist and aren't a known trap or disposable address — before you add it to a campaign. It is the single most effective way to control bounce rate.
Cold email deliverability is the share of your outbound cold emails that actually reach the recipient's inbox (not spam, not blocked). It depends on domain authentication (SPF, DKIM, DMARC), sender reputation, mailbox warmup, list hygiene and content — not just whether the email was 'sent'.
DMARC (Domain-based Message Authentication, Reporting & Conformance) is an email standard that tells receiving mail servers what to do with messages that fail SPF or DKIM checks — and sends you reports. It prevents spoofing of your domain and is now effectively required by Gmail and Yahoo for bulk senders.