Bounce codes

A contact is marked as bounced when their receiving email server rejects an email campaign or automation email. This rejection can mean that the email address is invalid or their inbox is inaccessible at the time of send.

There are two types of bounces that we track: hard bounces and soft bounces.

A hard bounce is a permanent failure or rejection. Once we receive a hard bounce, we mark the contact immediately as “Bounced” and we will no longer send any campaigns or automation emails to them.

A soft bounce is a temporary failure or rejection. Some reasons may include:

  • Their server is unavailable or down
  • Their server is overloaded
  • The recipient’s mailbox is full
  • The message size is too big
  • Failing email authentication

When a contact soft bounces, we don't mark the contact as bounced until this happens three times in a row (3 separate campaigns). If we receive three soft bounces for your contact, they are marked as “Bounced” and we will no longer send them any campaigns or automation emails.

When a contact bounces, we will list the date of the bounce, the bounce code, the type of bounce (hard or soft), and the bounce description in your campaign and automation email reports:

The bounce codes displayed on your report page are the codes that our servers receive from the recipients’ mail servers. Please note that it’s possible that these receiving mail servers may provide codes that do not accurately reflect the true nature of the bounce.

Below is a list bounce codes that we use and support:

Bounce Code Bounce Type Description
4.2.2 Soft The email account is over quota
5.0.0 Hard Address does not exist
5.1.0 Hard Other address status
5.1.1 Hard Bad destination mailbox address
5.1.2 Hard Bad destination system address
5.1.3 Hard Bad destination mailbox address syntax
5.1.4 Hard Destination mailbox address ambiguous
5.1.5 Hard Destination mailbox address valid
5.1.6 Hard Mailbox has moved
5.1.7 Hard Bad sender\'s mailbox address syntax
5.1.8 Hard Bad sender's system address
5.2.0 Soft Other or undefined mailbox status
5.2.1 Soft Mailbox disabled, not accepting messages
5.2.2 Soft Mailbox full
5.2.3 Hard Message length exceeds administrative limit.
5.2.4 Hard Mailing list expansion problem
5.3.0 Hard Other or undefined mail system status
5.3.1 Soft Mail system full
5.3.2 Hard System not accepting network messages
5.3.3 Hard System not capable of selected features
5.3.4 Hard Message too big for system
5.4.0 Hard Other or undefined network or routing status
5.4.1 Hard No answer from host
5.4.2 Hard Bad connection
5.4.3 Hard Routing server failure
5.4.4 Hard Unable to route
5.4.5 Soft Network congestion
5.4.6 Hard Routing loop detected
5.4.7 Hard Delivery time expired
5.5.0 Hard Other or undefined protocol status
5.5.1 Hard Invalid command
5.5.2 Hard Syntax error
5.5.3 Soft Too many recipients
5.5.4 Hard Invalid command arguments
5.5.5 Hard Wrong protocol version
5.6.0 Hard Other or undefined media error
5.6.1 Hard Media not supported
5.6.2 Hard Conversion required and prohibited
5.6.3 Hard Conversion required but not supported
5.6.4 Hard Conversion with loss performed
5.6.5 Hard Conversion failed
5.7.0 Hard Other or undefined security status
5.7.1 Hard Delivery not authorized, message refused
5.7.2 Hard Mailing list expansion prohibited
5.7.3 Hard Security conversion required but not possible
5.7.4 Hard Security features not supported
5.7.5 Hard Cryptographic failure
5.7.6 Hard Cryptographic algorithm not supported
5.7.7 Hard Message integrity failure
9.1.1 Hard Hard bounce with no bounce code found. It could be an invalid email or rejected email from your mail server (such as from a sending limit).
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