Hard Bounce
A hard bounce is a permanent delivery failure indicating the email cannot be delivered. Common causes include non-existent email addresses, closed accounts, invalid domains, or the receiving server permanently blocking delivery. Hard bounced addresses should be immediately suppressed from future sends.
Impact on Sender Reputation
High hard bounce rates (above 2-3%) signal poor list quality to mailbox providers. This damages your sender reputation and can lead to throttling or blocking. Email validation before sending reduces hard bounces by catching invalid addresses, typos, and disposable emails before they enter your list.
Related Terms
Soft Bounce
A temporary email delivery failure that may resolve on retry, such as a full mailbox or server timeout.
Bounce Rate
The percentage of sent emails that couldn't be delivered to the recipient.
List Hygiene
The practice of maintaining a clean email list by removing invalid and inactive addresses.
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