What is a bounce, and how can I prevent it?

This article explains what a bounce is, the causes and consequences of a bounce, and how to address and reduce bounces effectively.

A bounce occurs when an email cannot be delivered to a recipient's inbox. When this happens, the email is essentially "bounced back," indicating that it was rejected and not received by the recipient.

There are two main types of bounces: soft bounces and hard bounces. Below are the most common reasons for a bounce:

1. Hard bounces (Permanent failure)

• The email address does not exist: Bounce codes start with 5xx. Hard bounces occur when email providers shut down inactive accounts or when the email address is invalid.

• In Marketune: Contacts with a hard bounce are marked as 'Rejected' and can no longer receive emails.

2. Soft bounces (Temporary failure)

• Temporary issues: Bounce codes start with 4xx or 5xx. Examples include:

• Full inboxes.

• Temporary server problems with the recipient's email provider.

• Contacts marked as 'Rejected' after three consecutive soft bounces with different emails.

• Marketune won’t retry sending the same email to contacts with a soft bounce unless the error message is 'try again later'.

Other causes of bounces:

• Sender reputation: A poor reputation due to high spam complaints can cause providers to block your emails.

• Message content: Spam-sensitive phrases, poor images, or links to malware websites can lead to email blocks.

• Improper DMARC records: Restrictive DMARC records (e.g., 'p=reject') without proper DKIM setup can result in bounces. You can use a tool like this one to check your DMARC record. 

• Free sender email addresses: Emails sent from free domains (e.g., @gmail.com, @yahoo.com) are more likely to bounce.

• Invalid email addresses: Obvious spam addresses (e.g., 123456789@invalid.com) are automatically rejected. These contacts will be shown in the report as a bounce with a 9.1.5 bounce code.

1. Filter by status: Go to 'Contacts' and filter for contacts with the ‘Bounced’ status.

2. View bounce details: Check the 'Reports' section for campaigns, click on 'Bounces' under the 'Summary' tab, and view the associated bounce codes.

If a contact has the 'Bounced' status, you can use the bounce code to identify the cause of the bounce. Here’s how to find the bounce code for a contact:

1. Go to the Reports section:
   Navigate to 'Reports' in your Marketune account.

2. View bounces for a specific campaign:

• Select a campaign.

• Click on 'Bounces' under the 'Summary' tab.

3. Locate the bounce code:

• The bounce code for each bounced email is listed under the 'Code' heading.

The bounce codes displayed in the reports are provided by the recipients' mail servers. Note that sometimes these codes may not fully explain the actual cause of the bounce. The table below lists common bounce codes in Marketune and their explanations:

4.2.2 - Soft

The mailbox is full because the recipient has exceeded an administrative quota or physical capacity per mailbox.

5.0.0 - Hard

The email address does not exist.

5.1.0 - Hard

Your email ID is blocked by the recipient.

5.1.1 - Hard

The left part of the email address (before the '@') is invalid.

5.1.2 - Hard

The domain, the right part of the email address (after the '@') is invalid.

5.1.3 - Hard

The complete email address is invalid.

5.1.4 - Hard

The receiving email address points to more than one email inbox, and the recipient's email provider does not know which one to use.

5.1.5 - Hard

The email cannot be delivered even though the receiving email address is valid. Adjustments to the message are necessary to ensure delivery.

5.1.6 - Hard

The receiving email address no longer accepts emails, even though it used to do so in the past.

5.1.7 - Hard

The sender's address is invalid. This can apply to any part of the email address.

5.1.8 - Hard

The sender's email system does not exist or cannot accept bounce-back emails.

5.2.0 - Soft

There is an issue with the recipient's email inbox. The mailbox exists, but something unidentifiable in the receiving mailbox caused this bounce.

5.2.1 - Soft

The mailbox exists but does not accept messages. This could be temporary or permanent.

5.2.2 - Soft

The mailbox is full because the recipient has exceeded an administrative quota or physical capacity per mailbox.

5.2.3 - Hard

The message is longer than what the recipient's email system allows.

5.2.4 - Hard

The mailbox is experiencing an issue with the mailing list system, preventing message delivery.

5.3.0 - Hard

There is an unknown issue with one or more recipient email systems.

5.3.1 - Soft

The message cannot be delivered because the recipient's email system is out of space.

5.3.2 - Hard

One or more recipient email systems are not accepting messages due to shutdown, excessive load, or maintenance.

5.3.3 - Hard

The message contains features not supported by the receiving system.

5.3.4 - Hard

The recipient's email provider has a maximum message size, and the message exceeds this limit.

5.4.0 - Hard

There is an unknown issue with the network connection between email providers.

5.4.1 - Hard

The recipient's email provider did not respond to the sender's connection request.

5.4.2 - Hard

The outgoing connection could not complete the message transaction due to a timeout or poor connection quality.

5.4.3 - Hard

A network issue prevented the recipient's email provider from delivering the message.

5.4.4 - Hard

Network issues at the recipient's email provider are limiting message routing.

5.4.5 - Soft

The email system could not deliver the message due to network congestion.

5.4.6 - Hard

A network issue caused a routing loop, resulting in the message being forwarded repeatedly.

5.4.7 - Hard

The message was considered too old by the receiving system and was delayed during processing.

5.5.0 - Hard

The sender's email server encountered an unknown technical issue.

5.5.1 - Hard

The sender's email server used an unsupported command.

5.5.2 - Hard

The sender's email provider used a command not recognized by the receiving system.

5.5.3 - Soft

The message was addressed to more recipients than the email systems could handle.

5.5.4 - Hard

A valid mail transaction protocol command was issued with invalid arguments.

5.5.5 - Hard

There was a mismatched protocol version that could not be automatically resolved.

5.6.0 - Hard

The message could not be delivered due to unknown reasons related to content or attachments.

5.6.1 - Hard

The recipient's email provider rejected the content or attachments of the message.

5.6.2 - Hard

The message contained content that required conversion, which the email system is not allowed to perform.

5.6.3 - Hard

The message contained content that required conversion, which the email system was unable to perform.

5.6.4 - Hard

The message contained content that required conversion, causing information loss.

5.6.5 - Hard

The message contained content requiring conversion that was not completed.

5.7.0 - Hard

The message caused a security issue, though the exact cause is unclear.

5.7.1 - Hard

The recipient's email provider does not accept messages from this sender due to security or policy issues.

5.7.2 - Hard

The recipient's email provider blocked the sender from posting messages to the mailing list.

5.7.3 - Hard

Security protocol issues between the sender's and recipient's email programs caused the bounce.

5.7.4 - Hard

There was an issue with the sender's user authentication.

5.7.5 - Hard

The sending system had issues with its DKIM authentication.

5.7.6 - Hard

The sender's email server struggled with processing the security features of the message.

5.7.7 - Hard

The sender's email server encountered issues processing the security features of the message, possibly due to corruption during transmission.

9.1.1 - Hard

Hard bounce without a specific code. This could indicate an invalid email address or a rejection due to server limitations.

For a detailed explanation of bounce codes, refer to the list above. Based on the code, you can identify the specific reason for the bounce and take the necessary action.

Bounces can impact your email deliverability and sending reputation:

• Negative impact: High bounce rates increase the likelihood of your emails being marked as spam.

• Positive impact: Maintaining a low bounce rate (0.5%-1%) helps build a strong sending reputation, improving deliverability.

Your bounce ratio might temporarily increase or spike due to various reasons, such as importing an outdated mailing list with inactive contacts, triggering spam filters, or having many recipients mark your email as spam. 

Since your bounce ratio directly impacts your sending reputation and email deliverability, it’s essential to keep it as low as possible. Below are some tips to help you manage this proactively:

1. Configure DMARC settings: Ensure your DMARC, SPF, and DKIM records are correctly set up.

2. Use double opt-in: Double opt-in helps prevent invalid email addresses caused by typos or bots and confirms that subscribers actively manage their accounts and want to hear from you. This is enabled by default in Marketune forms.

3. Add CAPTCHA: Include CAPTCHA in your forms to block bots from signing up, even if double opt-in is enabled.

4. Send emails regularly: Inactive email addresses may bounce, and long gaps in communication can lead recipients to forget you, increasing spam complaints. Consistent emailing helps prevent this.

5. Use engagement tagging automations: Marketune offers pre-built Engagement Tagging automations that classify contacts as 'Engaged,' 'Disengaged,' or 'Inactive' based on their interactions. Use these tags for segmentation, list cleaning, and triggering automations.

6. Verify email addresses: Use real-time verification services like Briteverify to ensure email validity, especially if you handle high volumes of sign-ups daily.

1. Soft bounces:

• These often resolve on their own due to temporary issues like a full inbox.

• If a contact has three consecutive soft bounces, reach out to confirm their email status. They may not be aware their inbox is full.

2. Hard bounces:

• Hard bounces require manual intervention.

• Use the bounce codes to identify the issue and take appropriate action (e.g., updating or removing invalid addresses).

If you believe a bounce is invalid—such as an error incorrectly marking a valid email address—contact Marketune support for assistance.