Email Bounce Types

While there are two primary categories of bounces, soft and hard, there are several types of bounces with each category.

Bounce Definition

Emails are message communicated between servers – mail servers to be specific. When an error occurs during this communication, a status notification is sent back to the sending server with a message about why the message could not be delivered. This is the bounce message.

Soft Bounce Types

As a reminder, soft bounces are treated as temporary bounces. Common types are:

Challenge Response

This recipient wants future sends to be authorized previous senders. This results from anti-spam software being used to challenge the sender of the email as a means of authorization.

DNS Failure

This tends to be a mail server issue, as in the server is down or not responding.

General Bounce

This type is too general to classify as it is often missing information to classify the bounce properly therefore we classify it as a soft bounce to try again.

Mailbox full

The mail server cannot deliver your email as the recipient’s inbox is full.

Mail block — spam detected

Your emails are blocked as they are deemed to be spam by the recipient’s mail server. This can be for content reasons, sender reputation or reply-to email address

Message too large

The size of your email, which includes all headers, text and images, is greater than the maximum size the recipient’s email system allows. We often do not know the allowable size so minimizing the size is preferred.

Transient bounce

The recipient mail server can’t deliver your email, but will retry for a limited period of time as the recipient mail server may accept the message in a subsequent retry attempt.

Hard Bounce Types

These are permanent deliver failures. The common types are:

Mail block — general

The mail server for the recipient is blocking email from DDC’s email servers completely. These emails are even attempted by the receiving email server to be delivered. This often is the result of blacklisting one or more of the following:

• The reply-to address

• One of our mail server IP addressed

• One of our sending email domains is blacklisted (most often temporarily)

• We must be an official whitelist sender

We may attempt to retry email in certain instances depending on the block reason. Please contact your account team if you require additional details.

Mail block — known spammer

The mail server receiving email for this recipient(s) has determined your sending reputation to be poor and that of spam.

Mail block — relay denied

This type typically occurs when the sender’s mail messages cannot be authenticated and therefore the email messages cannot be transmitted. Sometimes this is the result of user error so if you see this error please check with support or your account team.