What are the bounce error categories and filters

If an email bounces, it means there is a permanent or temporary reason the email could not be delivered. Unless stated otherwise, the Elastic Email system will attempt to send the email for up to 48 hours. If it remains undelivered after this window, it registers as a "bounced" message.

Emails with 5xx bounce error codes are permanent failures and will not be retried. Emails with 4xx error codes are temporary and are retried automatically.

To protect your sender reputation, a contact that bounces 7 emails in a row will automatically have its status changed to Invalid. For more details, see our article on How To Manage Subsequent Bounces.

When an email is not successfully delivered, it is grouped into one of the following categories.

NoMailbox

The address does not appear to exist. It may be misconfigured or removed from its server. Receiving this error will permanently turn the contact's status to Invalid.

Spam

The email was rejected because it matched a profile the internet community has labeled as Spam or was caught by the recipient's anti-spam filters.

BlackListed

The email bounced due to the sender's IP address being blacklisted. Our system automatically applies an exponential backoff algorithm to mitigate this.

Throttled

The recipient server did not accept the email within the delivery window, often due to exceeding rate limits (e.g., error code S3150).

GreyListed

The recipient server has temporarily rejected the email (triplet check) to verify the sender's validity. Our system retries these automatically.

AccountProblem

There is an issue with the recipient's mailbox, such as being full or inactive. For 5xx errors, the contact is added to the block list.

DNSProblem

The domain part of the email address does not exist or could not be resolved.

SPFProblem

The email failed SPF authorization.

Timeout

The delivery failed because a connection timeout occurred between our servers and the recipient.

ConnectionProblem

A general issue occurred during the SMTP session between Elastic Email and the recipient server.

ConnectionTerminated

The recipient server dropped the connection during the data transmission phase.

NotDelivered

An internal block occurred. This happens if the contact is already on your block list, unsubscribed, or if a "Transactional only" contact is sent a non-transactional email.

NotDeliveredCancelled

The message was cancelled after 48 hours of continuous throttling or was blocked due to abuse detection.

ManualCancel

The email was manually cancelled by a user or an Elastic Email administrator.

CodeError

A system-level error occurred (e.g., an empty message body).

Unknown

A "catch-all" category for SMTP responses that do not match any existing rules. This includes route errors or unusual filter responses.

Ignore

Internal resource errors on the recipient's side, such as "insufficient system storage" (4.3.1).

If a contact has a "Transactional only" status, you must ensure your emails are flagged correctly, or they will be blocked internally with the category NotDelivered.

In the REST API, there is no isTransactional parameter. Instead, the message type is determined by the endpoint you use:

Add a custom header to your email. The header is case-insensitive:

isTransactional: true

When creating a campaign in the dashboard, select the campaign type as "Transactional" in the sending settings.