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Bounce Classification Codes

Last updated February 2020

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

1UndeterminedThe response text could not be identified.Undetermined
10Invalid RecipientThe recipient is invalid.Hard
20Soft BounceThe message soft bounced.Soft
21DNS FailureThe message bounced due to a DNS failure.Soft
22Mailbox FullThe message bounced due to the remote mailbox being over quota.Soft
23Too LargeThe message bounced because it was too large for the recipient.Soft
24TimeoutThe message timed out.Soft
25Admin FailureThe message was failed by SparkPost's configured policies.Admin
30Generic Bounce: No RCPTNo recipient could be determined for the message.Hard
40Generic BounceThe message failed for unspecified reasons.Soft
50Mail BlockThe message was blocked by the receiver.Block
51Spam BlockThe message was blocked by the receiver as coming from a known spam source.Block
52Spam ContentThe message was blocked by the receiver as spam.Block
53Prohibited AttachmentThe message was blocked by the receiver because it contained an attachment.Block
54Relaying DeniedThe message was blocked by the receiver because relaying is not allowed.Block
60Auto-ReplyThe message is an auto-reply/vacation mail.Soft
70Transient FailureMessage transmission has been temporarily delayed.Soft
80SubscribeThe message is a subscribe request.Admin
90UnsubscribeThe message is an unsubscribe request.Hard
100Challenge-ResponseThe 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.

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