Signal & Syntax · Email deliverability

What Is a Soft Bounce?

A soft bounce is a temporary email delivery failure. A full mailbox, an offline server or greylisting returns a soft bounce.

Also calledtemporary bounce

Example

452 4.2.2 Mailbox full

Soft Bounce in Practice

Soft bounces arrive with a 4xx status code. The sending server retries on a schedule. An address that soft-bounces on every send for weeks behaves like a hard bounce. Sending platforms convert repeated soft bounces into suppressions.

Where ScoreMachine Fits

score.email.validation

smtp_status_code

smtp_status_code shows whether the server's answer was temporary or permanent.

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Related Terms

Hard bounce A hard bounce is a permanent email delivery failure. SMTP status codes SMTP status codes are three-digit mail server replies. SMTP SMTP (Simple Mail Transfer Protocol) is how mail servers send email to each other. Sender reputation Sender reputation is the standing mailbox providers give a sending domain and IP.

Read the Guide

Guide

MX Records, SMTP Codes and Bounces Explained

How an email finds a mailbox, and how the server answers. Read the guide →

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