A bounce is basically a rejected email. When you send your campaign, When the email gets to the receiving server (where your subscriber’s email is located), the receiving mail server either accepts the email or rejects it. The rejection is called a Bounce.
There are 2 types of bounces: Soft and Hard.
A soft bounce normally happens when the receiving Mail Server is temporarily unable to receive the email. There are several reasons why this would happen. The following are reasons for soft bounces.
Soft bounces would normally resolve itself.
A hard bounce is more permanent.
There are several reasons why an email would hard bounce. The main characteristic though, is that it is a permanent rejection. Below is a list of bounce codes that's available.
Bounce code | Bounce type | Description |
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). |
As a note, the bounce codes displayed on this list are the codes that servers receive from the receiving mail servers. It is important to know that it’s possible that these mail servers may provide codes that do not really reflect the true nature of the bounce.
Brilliant overview, thank you for sharing!