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What's the definition of the different types of bounces?

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Here's a full rundown of each of the types of bounces you might see in your Bounce Activity Report.

Auto Reply (AR)

These are soft bounces caused by an automatic response from the recipient, for example "Out Of Office" messages. The email is still actually delivered to the inbox, and once the subscriber opens the email (and is recorded), the bounce is removed from your reports.

General Bounce (GB)

The email server could not deliver your email message, but the bounce processing tool could not determine a specific reason for the bounce. Normally that is because the bounce message from the recipient's server was very broad. We treat these as soft bounces.
Example: "Subject: Undeliverable mail"

Hard Bounce (HB)

A bounce where the message is considered permanently undeliverable, but the recipient's server has not provided a specific bounce reason. Hard bounces are automatically removed from your subscriber lists so you don't pay to send to them again.

Soft Bounce - General (SB)

The email server is temporarily unable to deliver your message to the recipient email address.
Example: "Connection timed out."

Soft Bounce - Dns Failure (SBDF)

The email server is temporarily unable to deliver your message to the recipient email address because of a DNS problem.
Example: "Host is unreachable"

Soft Bounce - Mailbox Full (SBMF)

The email server is temporarily unable to deliver your message to the recipient email address because the recipient's email box is full.
Example: "Mailbox over quota"

Soft Bounce - Message Size Too Large (SBMS)

The email server could not deliver your message to the recipient because the message size is too large.
Example: "Exceeded maximum inbound message size"

Transient Bounce (TB)

The email server temporarily can not deliver your message, but it is still trying.
Example: "Warning: message still undelivered after 4 hours. We will keep trying until message is 2 days old"

Mail Block - Attachment Detected (MBAD)

Indicates that the recipient's email server is blocking your email because it contains an attachment.
Example: "552 Disapproved attachment"

Mail Block - Relay Denied (MBRD)

Indicates that the recipient's email server is blocking email from our email server.
Example: "551 relaying denied"

Non Bounce (NB)

We determined that the message was not a bounce. This could be a recipient reply, or maybe a bounce format that we didn't recognize.

Mail Block - General (MB)

Indicates that the recipient's email server is blocking email from our email server.
Example: "550 Message REFUSED by peer"

Mail Block - Known Spammer (MBKS)

Indicates that the recipient's email server is blocking your email because it believes you are a spammer.
Example: "REJECT Known SPAM source"

Mail Block - Spam Detected (MBSD)

Indicates that the recipient's email server is blocking your email because the message appears to have content that looks like spam.
Example: "550 Possible spam detected"

Subscribe Request (SR)

A message has been sent back to the bounce address, looking to be added to your list. Since actual people would not normally know this address, these messages are just considered soft bounces.

Unsubscribe Request (UR)

In the same way as Subscribe Requests, these messages to unsubscribe sent to the bounce address are considered bounces. Actual subscribers will click the unsubcribe link or use the 'reply-to' address.

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  • Updated: Friday 22nd Sep 2017