Email Bounce Types in Keap: What They Mean and How to Fix Them – Keap Max Classic

When an email cannot be delivered, it bounces. Understanding why an email bounced helps you take the right corrective action — whether that means cleaning your list, adjusting your email content, or fixing your domain authentication settings. When an email bounces, the recipient's server sends a message back describing the reason. Keap records this reason and assigns a bounce type so you can identify and address the issue.

This article covers every bounce type you may encounter in Keap, what causes each type, and how to reduce excessive hard bounces. This article does not cover how to view bounce data in your reports. To find bounce information for your account, navigate to the Email Engagement Tracker under Reports if you are on a Pro or Max plan, or navigate to the Email Status Search under Marketing then Reports if you are on a Classic plan.

General Bounce

A general bounce occurs when a receiving mail server is unable to deliver a message but does not provide a specific diagnostic code explaining why. In most cases, a general bounce reflects a soft bounce condition.

Typically, the receiving server initially accepts the message. However, shortly after the sending server closes the SMTP connection, the receiving system generates a bounce notification. Because the connection is already closed at that point, the bounce is sent out of band — meaning it travels back through a separate channel — and in many cases it never makes its way back to Keap. Without that return path, Keap cannot capture the underlying SMTP error, so the event is recorded as a general bounce.

These out-of-band (OOB) bounces are common across the email industry and generally indicate temporary issues on the receiving domain's side, such as throttling, reputation filtering, or transient mailbox or server problems.

Hard Bounce

A hard bounce is recorded when an email message is considered permanently undeliverable. When a hard bounce occurs, the system will not attempt to deliver the email again. Hard bounce email addresses are automatically disabled — the system will not send any automated marketing emails to a hard bounced address going forward.

Hard bounces can occur for the following reasons:

The email address does not exist at the receiving domain.
The email is being rejected due to authentication issues with your sending domain.
The email is being blocked due to content or sender reputation issues.
The email address is on a restricted sending list.

Too many invalid hard bounces can damage your sender reputation. While there is no agreed-upon industry standard rate for hard bounces, Keap considers a hard bounce rate above 5% per email provider to be excessive. Accounts generating excessive hard bounce rates are at risk of being contacted by the Keap Email Compliance Team.

Soft Bounce

A soft bounce occurs when a message cannot be delivered due to a temporary issue with the recipient's mailbox or receiving server. Keap does not surface soft bounces directly in your reports. Instead, messages that soft bounce are placed into a 12-hour retry queue where the system makes multiple delivery attempts automatically.

If delivery is still unsuccessful after 12 hours, the message is removed from the retry queue and recorded as a Hard Bounce (Timeout). In these cases, Keap records both the timeout status and the original soft bounce reason so you have full visibility into what happened. Many receiving mail systems will continue attempting redelivery internally for hours or days after the initial failure, but from Keap's perspective, the message becomes undeliverable once the retry queue expires.

Common Types of Soft Bounces

Mailbox Full — The recipient's mailbox has exceeded its storage quota. This typically indicates poor mailbox maintenance but may also signal an inactive or abandoned email account.
Message Too Large — The email exceeds the maximum acceptable message size set by the receiving server. This is usually caused by large attachments or embedded content in the email.
DNS Failure — The receiving server cannot be located because DNS records needed for delivery cannot be resolved. This usually reflects a DNS misconfiguration on the recipient's domain rather than an issue with your sending setup. SPF, DKIM, or DMARC misalignment can also contribute to DNS failure soft bounces in some cases.
General — A temporary delivery failure occurred but the receiving server did not provide a specific SMTP error code explaining the reason.

Mail Blocks

A mail block is recorded when the receiving mail server rejects a message before attempting inbox delivery. A mail block is an immediate SMTP-level rejection — not a temporary failure. When a mail block occurs, Keap does not retry delivery. The recipient's marketability status is not affected by a mail block, and you may manually resend the message once the underlying issue is resolved.

Types of Mail Blocks

General — The receiving server is blocking messages originating from Keap's sending infrastructure. No specific reason is provided by the receiving server.
Known Spammer — The receiving server is rejecting your message due to sender reputation issues tied to your domain, IP address, or historical sending patterns. The recipient's mail system has determined that your mail resembles spam based on your sending history.
Relay Denied — The receiving server will not accept the message for relay from Keap's sending infrastructure. Adding infusionmail.com to your SPF record may help reduce relay denied blocks by clarifying that Keap is an authorized sender for your domain.
Spam Detected — Content-based filters on the recipient's server are identifying your email as spam. Use the Spam Score tool in the Keap email builder to evaluate and reduce potentially flagged content. A spam score under 5 — ideally 0 — is recommended before sending.
Attachment Detected — The receiving server rejected the message because of the attachment included in the email. Possible causes include:
- The file type is restricted by the receiving server (for example, .exe files).
- The receiving server does not allow attachments at all.
- The attachment was flagged as a potential malware source.
- The attachment file size exceeds the receiving server's limit. Keep attachments under 10 MB to avoid this block type.

Mail blocks indicate policy-based rejection by the receiving server and typically require adjustments to your email content, domain authentication setup, or sending practices before the message can be delivered successfully.

Unsubscribe Request

An unsubscribe request is recorded when a recipient sends an auto-reply message to Keap's bounce capture address — mailer@infusionsoft.com or bounce@infusionsoft.com — asking to be removed from your email list. This can happen when a real person replies to your email asking to be removed, or when a recipient clicks the Unsubscribe link in your email. Unsubscribe requests are treated the same as an ISP spam complaint and result in the contact being marked as opted out.

Undetermined

An undetermined status is assigned when Keap cannot identify the cause of the bounce based on the feedback received from the receiving server. The receiving server returned an error, but the error code or message did not match any recognized bounce category. No action can be taken on an undetermined bounce beyond monitoring whether the issue recurs for the same address.

Invalid Address Bounces

An Invalid Hard Bounce occurs when you attempt to send email to an address that does not exist or is otherwise undeliverable at the receiving mailbox provider. The mailbox provider returns a permanent 5xx failure response indicating the address is invalid. Future attempts to send to that address will always fail — the address cannot be re-enabled for sending.

Common Causes of Invalid Address Bounces

Sending to a cold email list — A cold list is one where no emails have been sent for a significant period of time. Many contacts change their email address regularly and may do so without notifying you. Sending regular emails helps you identify address changes before contacts fully disengage, giving them the opportunity to resubscribe with their new address.
Purchased or scraped lists — Lists that were purchased or scraped from the web typically contain a significant number of invalid email addresses. Generating your list organically through lead collection is strongly recommended. Any account known to have imported a purchased or scraped list is at risk of account suspension.
Invalid lead generation information — Web forms are a common source of invalid email addresses. Contacts who want access to gated content but do not want to receive marketing emails frequently enter fake email addresses into web forms. Implementing email verification on your web forms helps reduce the number of invalid addresses entering your list.
List bombing — List bombing occurs when an automated bot randomly fills out your web forms with obscure or nonexistent email addresses. Protecting your web forms from bot attacks reduces list bombing exposure.

How to Reduce Your Hard Bounce Rate

If you have received a message from the Keap Email Compliance Team about excessive invalid hard bounces, take the following steps to identify the source and reduce your bounce rate. Failure to address excessive hard bounces may result in account suspension.

Perform list hygiene to identify and remove invalid, inactive, and unengaged email addresses from your contact list.
Audit your landing pages and web forms for unsecured entry points that may be accepting fake or bot-submitted email addresses.
Review your lead collection process to identify where invalid email addresses are entering your list and implement verification steps to improve the quality of incoming leads.
Review the Email Compliance Best Practices Guide and implement the recommended improvements to your sending practices.

Trusted Partners for Email Deliverability and List Hygiene

If you want professional guidance on improving your email practices or tools to help maintain a clean, healthy list, the following trusted partners specialize in email deliverability and list hygiene:

Email Deliverability Training, Consulting, and Software

EmailSmart — deliverability specialist training, consulting, and software

List Cleaning

Form Security