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. You can view the bounce type in the Email Status Report (Marketing > Reports > Email Status Report). You can also set up actions that trigger each bounce type (Marketing > Settings > Template Settings and click on the Email Status Automation tab). You can use these actions to segment people based on bounce issues and follow up with individuals to request a new email address or resolve the problem that is preventing email delivery.

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. These are called Out of Band bounces.

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.  This can be due to the email address not existing,  your mail is being rejected due issues with the authentication of you mail, or the mail is being blocked due to content/reputation related issues. You will also see a Hard Bounce if the email address is on the Restricted sending list. Your sender reputation can be affected by too many invalid hard bounces.

Unlike spam complaint rates, there is currently no agreed upon industry standard rate when it comes to invalid hard bounces.   At Keap, we consider anything over 5% per email provider as excessive and at risk for being contacted by our Email Compliance Team.

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 ( or 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 an inbox. When we see a mail block like below, we do not make any further attempts to send the mail. However, you can attempt to send the mail again as there is no changes made to the marketability status of the email addresses that see bounces like these.

  • 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( or 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.

Potential causes of invalid addresses

  • Sending to a Cold Email List
    • A cold email list is one where there has been a significant amount of time since an email has been sent.  
    • Many customers change their email address every year and may change their address without you knowing.  
    • Sending regular emails helps catch customers before they change so they can resubscribe with their new address.
  • Purchased or Scraped Lists
    • Purchase or scraped lists typically have a significant amount of invalid email addresses.  
    • It is better to generate all email lists organically through lead collection.  
    • Warning:  Any account known to have imported a purchased or scraped list is in danger of having their account suspended.
  • Invalid Lead Generation Information
    • Web forms that include an email address can be the source of potential invalid email addresses.  Fake email addresses are frequently entered into web forms to get to the promised access to information. 
    • This typically happens when the potential customer isn't interested in getting spam from the company but really wants the content or promotion.
  • List Bombing
    • List bombing happens when a web bot randomly fills out web forms with obscure email addresses.  


If you have received an email from the Keap's Compliance Team about excessive invalid hard bounces being generated by your application then please read this section carefully and enact the measures needed to reduce your hard bounce rate.

  • List hygiene
  • Audit your landing pages and check for unsecured web forms
  • Audit your lead collection process for incoming invalid email addresses and take the steps needed to promote trust and loyalty to your prospective leads
  • Review the best practices guide and make improvements where necessary
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