Signal & Syntax · Email deliverability
What Is a Hard Bounce?
A hard bounce is a permanent email delivery failure. The mailbox or the domain does not exist, or the server refuses the mailbox.A hard bounce is a permanent email delivery failure. The mailbox or the domain does not exist, or the server refuses the mailbox.A hard bounce is a permanent email delivery failure. The mailbox or the domain does not exist, or the server refuses the mailbox.
Also calledpermanent bounce
Example
550 5.1.1 The email account does not exist
Hard Bounce in Practice
Hard bounces arrive with a 5xx code. A 5.1.x code marks a bad address, and 5.7.x a policy block. A hard-bounced address stays undeliverable, so the address comes off the list. Mailbox providers count hard bounces against the sender's reputation. Checking addresses before the send keeps hard bounces out of the campaign.Hard bounces arrive with a 5xx code. A 5.1.x code marks a bad address, and 5.7.x a policy block. A hard-bounced address stays undeliverable, so the address comes off the list. Mailbox providers count hard bounces against the sender's reputation. Checking addresses before the send keeps hard bounces out of the campaign.Hard bounces arrive with a 5xx code. A 5.1.x code marks a bad address, and 5.7.x a policy block. A hard-bounced address stays undeliverable, so the address comes off the list. Mailbox providers count hard bounces against the sender's reputation. Checking addresses before the send keeps hard bounces out of the campaign.
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Guide
MX Records, SMTP Codes and Bounces Explained
How an email finds a mailbox, and how the server answers. Read the guide →Run the Checks on Your Own List
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