Email bounces explained

This article applies to:

Most emails bounce because of a permanent issue with the receiving email account, a temporary issue with the receiving email account, or because the email is blocked by the receiving server. 

When an email bounces, the recipient's server sends a message back to Keap that describes the reason for the bounce.

General Bounce

A general bounce is recorded when the server could not deliver an email message, but also could not detect a specific reason. In most cases, this is related to a soft bounce.

Hard Bounce

A hard bounce is recorded when an email message is considered permanently undeliverable. The email system will not try to deliver the email again. Hard bounce email addresses are automatically disabled. The system will not allow you to send any automated email to these accounts. You can contact the person directly to request a valid email address. 

In most cases, a hard bounce indicates the email address does not exist, however, it may also indicate that your emails are being rejected due to the SPF configuration on your DNS account. You may need to configure the SPF records to allow Keap servers to send email from you. For more information, click here

Soft Bounces

A soft bounce is recorded when there is a temporary issue with the recipient's email account, delaying message delivery. In many cases, the email system will try to redeliver the message several times over a period of hours or days and will only consider it undeliverable after the retry process times out. There are several types of soft bounces.

  • Mailbox Full: The recipient's email box is too full. There is no room for the message. Most of the time this is related to improper maintenance, but it could mean that the recipient no longer actively uses the email account even though it still exists.
  • Message too Large: There is content in the message or attachments causing the message size to exceed the limits of the receiving server.
  • DNS Failure: The email cannot be delivered due to an issue with the receiving server. This is most likely an issue with the nameserver settings for your domain. Contact your domain administrator for assistance. The issue may be related to the SPF records.
  • General: The specific reason for the bounce has not been detected.
  • Auto Reply: This kind of soft bounce indicates the message has been delivered, but the recipient has an auto-reply enabled on their account. The bounce status will be removed as soon as the recipient opens the email.
  • Subscribe Request: These are recorded when an auto-reply is sent to your bounce capture email account ([email protected] or [email protected]) asking to be added to your list. They are a type of soft bounce since most people would not send a message to these accounts.

Mail Blocks

A mail block is recorded when the recipient's email server blocks an email message completely. It rejects it before it tries to deliver it to their inbox.

  • General: The recipient's email server is blocking messages sent through the Keap server.
  • Known Spammer: The recipient's email server is blocking messages from your email account based on an email history or reputation that indicates you've been sending SPAM.
  • Relay Denied: The recipient's email server is blocking messages sent through the Keap server. Setting up your SPF to include will help you resolve this issue.
  • Spam Detected: The recipient's email server is blocking your email because the content looks like SPAM. Use the Keap Spam Score tool in the email template to check the email content and reduce the SPAM score below 5 (preferably zero.)
  • Attachment Detected: The recipient's email server is blocking the message because of the attachment. It may have identified the attachment as a possible virus source, the system may not allow attachments at all, or may block specific types of files (e.g. .exe). The size of the attachment may also be causing an issue. Make sure your attachment size is less than 10 MB.

Unsubscribe Request

These are recorded when an auto-reply request is sent to your bounce capture email account ([email protected] or [email protected]) asking to be removed from your email list. A real person will reply to the email or click on the Unsubscribe Link. These Unsubscribe Requests are the same as an ISP Spam complaint.


An undetermined status is assigned when Keap is not able to identify the cause of the bounce based on the feedback received from the receiving server.