Bounce Classification Codes

July 23, 2018 Contributors

Following is a list of bounce classification codes and their meanings:

Classification Name Description Category
1 Undetermined The response text could not be identified. Undetermined
10 Invalid Recipient The recipient is invalid. Hard
20 Soft Bounce The message soft bounced. Soft
21 DNS Failure The message bounced due to a DNS failure. Soft
22 Mailbox Full The message bounced due to the remote mailbox being over quota. Soft
23 Too Large The message bounced because it was too large for the recipient. Soft
24 Timeout The message timed out. Soft
25 Admin Failure The message was failed by SparkPost’s configured policies. Admin
26 Smart Send Suppression The message was suppressed by Smart Send policy. Admin
30 Generic Bounce: No RCPT No recipient could be determined for the message. Hard
40 Generic Bounce The message failed for unspecified reasons. Soft
50 Mail Block The message was blocked by the receiver. Block
51 Spam Block The message was blocked by the receiver as coming from a known spam source. Block
52 Spam Content The message was blocked by the receiver as spam. Block
53 Prohibited Attachment The message was blocked by the receiver because it contained an attachment. Block
54 Relaying Denied The message was blocked by the receiver because relaying is not allowed. Block
60 Auto-Reply The message is an auto-reply/vacation mail. Soft
70 Transient Failure Message transmission has been temporarily delayed. Soft
80 Subscribe The message is a subscribe request. Admin
90 Unsubscribe The message is an unsubscribe request. Hard
100 Challenge-Response The message is a challenge-response probe. Soft

Note that soft, block and undetermined are usually temporary events. If you’d like to filter on suppression-level events, only check for hard or admin bounce-type events.