Hard bounce is a permanent email delivery failure, usually because the address is invalid or does not exist.
In depth
Hard bounces should be removed from your list immediately; continuing to email them signals poor list hygiene to mailbox providers and damages deliverability. Common causes are typos at signup, closed accounts and non-existent domains. Double opt-in and address validation reduce them at the source, and most platforms suppress hard-bounced addresses automatically.
Example
Emailing an address at a domain that cannot receive mail returns a hard bounce.
Related terms
See our full email marketing glossary or the complete email marketing guide.