Learn how to locate bounce details, understand each major classification, identify affected contacts, determine where a correction needs to be made, and decide whether an email should be corrected, retried, or stopped.

Do not troubleshoot from the SMTP code alone. The same SMTP code can appear with different enhanced codes or provider responses. Review the classification, code, enhanced code, definition, and full delivery response together before deciding what to change.

Bounce classification organizes email delivery failures into categories that make the underlying problem easier to diagnose. A classification can point to an invalid recipient, an authentication problem, a full mailbox, a recipient-side restriction, poor sending reputation, or another mail-server response.

Bounce classifications turn a failed email into actionable troubleshooting information. Understanding the category helps you avoid repeatedly changing settings that are unrelated to the actual delivery problem.

• Faster Diagnosis: Identify whether the issue originates with the recipient, sending domain, content, rate limit, or reputation.
• Clearer Next Steps: Know whether to edit a contact, review DNS authentication, wait for a temporary condition, or contact the recipient.
• Better List Hygiene: Find invalid or unreachable addresses before repeated failures affect deliverability.
• Improved Sender Reputation: Reducing preventable bounces helps protect future email delivery.
• More Accurate Troubleshooting: Use the enhanced code and full error response instead of relying on a generic failed-delivery message.

The correct place to make an adjustment depends on the bounce category. Start with Bounce Classification to identify the problem, then use the appropriate area of the platform to correct the recipient, sender configuration, campaign, or domain.

Step 1: Review Bounce Classification

1. Open the affected sub-account.
2. Go to Settings → Email Services → Bounce Classification.
3. Review the highest-volume bounce categories.
4. Open the error details and note the category, SMTP code, enhanced code, provider, and full error message.

Step 2: Find the Affected Contacts

For contact-level email data, go to Settings → Email Services → Email Analytics. Select the applicable date range and email source, then use the Bounced metric to review affected contacts.

For a specific email campaign, go to Marketing → Emails → Campaigns, open the three-dot menu next to the sent campaign, and select Statistics. Review the hard- and soft-bounce details for that send.

Step 3: Make the Appropriate Adjustment

Use the classification as a routing tool. The table below shows the most appropriate next action after the bounce has been identified.

Blocked

A Blocked classification means a receiving system prevented delivery because of a rule or policy. The exact cause can include message-size restrictions, mailbox limitations, security policy, or another provider-specific rule.

DMARC

DMARC classifications indicate that the message failed an authentication or alignment check. The From domain should align with properly configured SPF and DKIM authentication for the sending domain.

Codes currently associated with this classification include:

Resolution Tips

1. Go to Settings → Email Services → Dedicated Domain and IP.
2. Confirm the sending domain is verified.
3. Review SPF and DKIM records and correct any missing or invalid DNS records.
4. Confirm the From email domain aligns with the authenticated sending domain.

Invalid Address

An Invalid Address classification generally means the recipient address does not exist, is inactive, is malformed, has already been identified as undeliverable, or cannot be reached because of a recipient-domain issue.

Common SMTP / enhanced-code combinations include:

Resolution Tips

1. Open the affected contact record.
2. Check for misspellings, extra spaces, an incorrect domain, or an outdated email address.
3. Replace the address only when a corrected or confirmed email is available.
4. Use Email Verification before sending to unverified lists or older contacts.
5. Do not repeatedly retry a hard-bounced address without correcting or revalidating it first.

Mailbox

Mailbox classifications indicate that the destination domain or address is not accepting mail as expected. This can occur when a mailbox does not exist, has been disabled, or the recipient domain is not configured to receive mail.

Mailbox Full

A Mailbox Full bounce occurs when the recipient's inbox has reached its storage limit and cannot currently accept another message. This is commonly a temporary condition rather than proof that the address is invalid.

Rate Limit

Rate Limit classifications occur when the receiving server throttles or rejects delivery because it is receiving messages too quickly or has applied another volume-related restriction.

Recipient Error

Recipient Error classifications usually indicate that the destination server rejected, restricted, timed out, or otherwise could not accept the message. These failures often require the recipient or their email administrator to review the destination environment.

Common code combinations include:

Rejection

Rejection is a broad category that can include invalid DNS or authentication records, sender-domain issues, oversized messages, mail loops, routing problems, or other provider-specific refusals. The enhanced code and full definition are especially important for this category.

How to Resolve Common Rejections

• DNS/authentication error: Go to Settings → Email Services → Dedicated Domain and IP and verify the domain and DNS records.
• Message too large: Reduce large images, attachments, or other content before sending again.
• Mail loop / too many hops: Review forwarding and routing configuration for the affected mailbox or domain.
• Provider-specific rejection: Use the complete error text to determine whether the sender or recipient administrator needs to make the correction.

Sender Reputation

Sender reputation reflects how receiving providers evaluate the trustworthiness of your sending domain and IP infrastructure. Poor reputation can cause otherwise valid messages to be throttled, blocked, rejected, or routed away from the inbox.

How to Improve Sender Reputation

1. Review Bounce Classification. Go to Settings → Email Services → Bounce Classification and identify the highest-volume problem categories.
2. Verify your sending domain. Confirm SPF, DKIM, and DMARC are correctly configured.
3. Clean your contact lists. Remove or correct invalid, stale, and repeatedly bouncing addresses.
4. Use Email Verification. Validate addresses before sending to older or uncertain lists.
5. Reduce sudden volume spikes. Build sending volume gradually instead of sending a large amount from a new or cold domain at once.
6. Send to engaged contacts. Prioritize recipients who expect and interact with your emails.
7. Monitor complaints and bounces. A worsening pattern should be investigated before additional bulk sends.
8. Review email content. Avoid misleading subject lines, suspicious links, overly promotional content, and emails that do not provide an easy way to unsubscribe.

Hard Bounce vs. Soft Bounce

Understanding whether a failure is permanent or temporary determines whether another delivery attempt is appropriate. Do not use only the first digit of the SMTP code to make this decision; use the platform's bounce type and final delivery state.

If you are not sure what to change, start by recording the bounce category, SMTP code, enhanced code, recipient provider, and complete error response. Those details determine whether the correction belongs on the contact, the sending domain, the email content, or the recipient's mail server.

• Invalid address: correct or replace the contact's email.
• DMARC/authentication: verify the sending domain and DNS configuration.
• Mailbox full / temporary error: allow the temporary condition and automatic retries to resolve.
• Recipient restriction: ask the recipient or their administrator to review the block.
• Sender reputation: review list quality, sending volume, authentication, complaints, and recent bounce patterns.
• Still unresolved: provide Support with the affected recipient, approximate send time, complete bounce response, classification, and screenshots of the issue.