Email Bounce Handling

The bounce compliance event type reflects the reason that an email server or recipient rejected your email as a bounce_class. The bounce class is a reason code between 1 and 100.

Airship automatically opts-out addresses that hard-bounce from a brand’s list. Hard bounces are represented in events with bounce_class values of 10, 30, or 90. These users will no longer receive emails from the brand, including business-critical emails. While other bounce_class values do not opt users out of emails, repeatedly sending messages to bounced email addresses will hurt a brand’s IP reputation and should be avoided.

If a brand has an email address that previously hard-bounced, but the inbox’s issue has been resolved, the brand can submit an Airship Support request to “unbounce” the address.

Bounce Classes


Hard bounce_class events (classifications 10, 30, and 90) result in an automatic opt-out for the delivery_address listed in the event.

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
26Smart Send SuppressionThe message was suppressed by Smart Send policy.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