Email bounce types

A bounced email is one which cannot be delivered to the recipient's email server. When this occurs, the recipient's email server will send an automated message called a Non-Delivery Report (NDR) with more details about the issue.

Bounces refer to issues with a specific recipient. If you are sending an email to multiple recipients, it may bounce for some contacts and be delivered for others. For marketing emails, you can learn more about which recipients bounced on the Recipients tab of the email performance page. 

Marketing emails

When contacts hard bounce on a marketing email, HubSpot drops them as recipients of future marketing emails. This protects your email sending reputation by preventing future bounces. If any valid contacts bounce on marketing emails, there's likely a security filter blocking the incoming message.

To resolve the problem:

1. Ask the contact to work with their IT team to add your sending IP addresses to their allowlist.
2. Once their IT team has added your sending IP address to their allowlist, unbounce the contact in your HubSpot account.

One-to-one emails

For emails sent through a connected inbox, bounce details are available in the email engagement on the contact timeline. A bounce for a one-to-one sales email sent from HubSpot CRM will display less information than a marketing email because it's sent through a connected inbox. You'll receive a bounceback email with the full bounce response in your own inbox.

Please note: HubSpot aims to detect bounces of one-to-one emails and emails sent through the sequences tool, but some bounced emails don't provide enough information for HubSpot to fully identify the root cause of the failed send. Bounces for emails sent outside of HubSpot will not be detected.

Types of bounces

• Hard bounce: usually indicates a permanent error, but can also be caused by a strict email security filter. To protect your email sender reputation, HubSpot excludes these contacts from future emails.
• Soft bounce: indicates a temporary problem with the recipient's server, or another temporary technical problem. Contacts who soft bounce are eligible to receive future emails.
• Pending bounce: caused by a temporary technical issue with either the sending or receiving email server. HubSpot continues to try sending the email for up to 72 hours. If the message isn't delivered during that time, it becomes a soft bounce.
• Global bounce: a hard bounce for a permanent reason across three or more HubSpot accounts. Permanent bounces include unknown user and mailbox full. Global bounces are dropped from future emails across all HubSpot accounts.

Hard bounce errors and recommendations

The possible reasons why a contact hard bounced are included below:

• Unknown user: this email address is invalid. HubSpot automatically drops contacts from future emails if they bounce for this reason. If a contact bounces for this reason across three HubSpot accounts, the email address is globally bounced.

• Mailbox full: an inbox that is inactive or has exceeded its storage quota for a long time. HubSpot automatically drops contacts from future emails if they bounce for this reason. If a contact bounces for this reason across three HubSpot accounts, the email address is globally bounced.

• Content: something in the email body or subject triggered spam filters. To solve the problem, ask the contact to add your sending IP addresses to their allowlist, then unbounce the contact in HubSpot.

• Spam: something in the body, subject, or From address of the email that is classified as spam by the recipient's email server. To solve the problem, ask the contact to add your sending IP addresses to their allowlist, then unbounce the contact in HubSpot.

• Policy: the email did not pass one of the security policies of the recipient's server, but it is not explicit about which one. This includes DMARC; DKIM, and SPF authentication failures. To solve the problem, ask the contact to add your sending IP addresses to their allowlist, then unbounce the contact in HubSpot.

• Other: this includes any global bounces, or if the response from the recipient's email server wasn't specific enough to categorize the bounce. To solve the problem, ask the contact to add your sending IP addresses to their allowlist, then unbounce the contact in HubSpot.

You can review the bounce details for a contact on the Recipients tab of a sent email:

1. In your HubSpot account, navigate to Marketing > Email.
2. Click the name of your email that included any contacts who bounced.
3. Click the Recipients tab.
4. In the left sidebar menu, click Bounced.
5. Click on a recipient to view more details about why they bounced. Under the Reason column, you can review the issue that HubSpot encountered when attempting to deliver your email to the recipient.

You can also view a contact's value in the Email hard bounce reason property. 

Please note: if an email to a contact globally bounced, but none of the emails you've sent to the contact from your HubSpot account have hard bounced, then the Email hard bounce reason property won't have an associated value.

Soft bounce errors and recommendations

• Temporary technical issue with the recipient's email: the recipient's server may be overloaded, timing out, or undergoing some configuration changes that prevented it from accepting the message. Create a clone of the original email and send it to the affected contacts at a later date. For a one-to-one sales email, try sending your message again at a later date.

• Rejected by recipient's email security filter: there's a temporary problem with the recipient's server or HubSpot's sending IP addresses. To solve the problem, ask the contact to add your sending IP addresses to their allowlist. Then create a clone of the original email and send it to the affected contacts at a later date. For a one-to-one sales email, try sending your message again at a later date.

• Your IT team has not authorized HubSpot to send emails on your behalf: your IT team set up a custom DMARC policy that needs to be updated to include HubSpot. Reach out to your IT team to send them documentation about using a DMARC policy with HubSpot.

• Temporary technical issue: there may have been a temporary technical problem with the recipient's email server or HubSpot's email server. Create a clone of the original email and send it to the affected contacts at a later date. For a one-to-one sales email, try sending your message again at a later date.

• Mailbox misconfiguration: the recipient's mailbox is temporarily unavailable, for reasons such as exceeding its storage quota for a short time.