Understanding Bounce Handling in MailerLogic

Email delivery doesn’t end when you hit Send. What happens after your message leaves the system directly impacts your sender reputation, analytics accuracy, and future deliverability.

This guide explains how bounce handling works in MailerLogic, what actions are taken automatically, and how you can monitor and manage bounce data effectively.

What Is Bounce Handling?

Bounce handling is the automated process of detecting, classifying, and managing email delivery failures.

When an email cannot be delivered, the recipient’s mail server returns a Non-Delivery Report (NDR) explaining the reason for failure. MailerLogic:

• Captures the bounce notification

• Identifies the original email and recipient

• Classifies the bounce type

• Applies the correct action automatically

• Updates your analytics and suppression list

This entire process happens in real time to protect your sender's reputation.

How MailerLogic Handles Bounces

1. Automatic Bounce Detection (Using VERP)

MailerLogic uses VERP (Variable Envelope Return Path) to track each email individually.

Example Email Headers

Return-Path: <b+customer-id+email-id+tracking-code@bounces.mailerlogic.net>
From: yourname@yourdomain.com

Each email sent through MailerLogic includes a unique Return-Path. When a delivery failure occurs, the bounce notification is sent back to that specific address. Because the Return-Path contains encoded information, it allows the system to accurately identify the associated customer ID, email ID, and tracking code. As a result, when a bounce is received, MailerLogic automatically links it to the exact original message and intended recipient without requiring any manual intervention.

2. Bounce Classification

MailerLogic classifies all bounces into two primary categories: hard bounces and soft bounces.

Hard Bounces (Permanent Failures)

A hard bounce represents a permanent delivery failure. This means the email address is invalid or will never be able to receive messages. Hard bounces typically occur due to issues such as a mistyped or non-existent email address, a domain that does not exist, or a mailbox that has been disabled or permanently deleted. In most cases, the receiving server returns standard SMTP error codes such as 550 5.1.1 (User unknown), 550 5.7.1 (Relay denied), or 553 5.3.0 (Domain does not exist).

When MailerLogic detects a hard bounce, the system immediately takes protective action. The email address is automatically added to your suppression list, all future sends to that address are blocked, the email status is updated to bounced, and an email.bounced webhook is trig

Soft Bounces (Temporary Failures)

Soft bounces indicate a temporary delivery issue rather than a permanent failure. In these cases, the recipient’s email address is valid, but the message could not be delivered at that specific time.

Soft bounces commonly occur when a mailbox is full, the receiving mail server is temporarily unavailable, the message exceeds the allowed size limit, or the server applies greylisting as a spam prevention technique. Typical SMTP error codes associated with soft bounces include 450 4.2.2 (Mailbox full), 451 4.3.0 (Temporary system error), and 452 4.5.3 (Message too large).

When MailerLogic detects a soft bounce, the event is logged for reporting and analysis, and delivery may be retried based on your configured retry settings. An email.bounced webhook is also triggered with "bounce_type": "soft". If the same address experiences three to five consecutive soft bounces, the system automatically suppresses it to protect your sender reputation. Soft bounces are monitored carefully before suppression to avoid unnecessarily removing valid contacts from your list.

3. Automatic Suppression List Updates

When a hard bounce is detected, MailerLogic immediately updates your suppression list to protect your sender reputation. The bounced email address is automatically added to the list and tagged with type: "bounce" and source: "automatic" to clearly indicate that it was system-generated due to a delivery failure. From that point forward, all future sends to that address are blocked to prevent repeated failed attempts. At the same time, your bounce metrics are updated in real time, ensuring that your analytics remain accurate and up to date.

You can review and manage suppressed email addresses at any time from your dashboard under Suppressions.

4. Real-Time Webhook Notifications

If webhooks are configured in your account, MailerLogic sends an immediate notification whenever a bounce occurs. This allows your systems to react in real time without waiting for manual review in the dashboard.

Example Webhook Payload

{
  "event": "email.bounced",
  "timestamp": "2026-02-26T20:58:35.000Z",
  "email_id": "a8e4b25a-2f4d-4fa7-87d2-bfb7890995f5",
  "recipient": "invalid@example.com",
  "bounce_type": "hard",
  "reason": "User unknown",
  "diagnostic_code": "550 5.1.1 User unknown",
  "tag": "campaign-welcome",
  "metadata": {
    "campaign_id": "welcome-2025"
  }
}

In this payload, the bounce_type field indicates whether the bounce is classified as "hard" or "soft". The reason provides a human-readable explanation of the failure, while the diagnostic_code contains the original SMTP response returned by the receiving server. The tag and metadata fields reflect any custom values you attached to the original email, making it easier to associate the bounce with a specific campaign, workflow, or business process.

By using webhook notifications, you can automatically sync bounce data with your CRM, update contact records instantly, trigger internal alerts, or initiate alternative communication workflows such as SMS or support follow-ups.

How to View Bounce Data

In the Dashboard

In your dashboard, go to the 'Overview' section and click 'Bounced' to view data on bounced emails.

Analytics

Go to 'Reports' → 'Analytics' and open 'Detailed Statistics' to view metrics such as 'Bounced', 'Hard Bounced', and 'Soft Bounced'.

Suppression List

Go to 'Deliverability' → 'Suppressions', select 'Bounce', and view all automatically suppressed addresses.

Via API

Get Bounce Statistics

curl https://api.mailerlogic.net/api/stats \
  -H "X-API-Key: your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "start_date": "2026-02-01",
    "end_date": "2026-02-28"
  }'

Get Specific Bounces

curl https://api.mailerlogic.net/api/bounces \
  -H "X-API-Key: your_api_key"

Get Suppression List

curl https://api.mailerlogic.net/api/suppressions?type=bounce \
  -H "X-API-Key: your_api_key"

Best Practices for Managing Bounces

• Review your bounce rate weekly and keep it below 2%; set up webhook alerts to detect sudden spikes early.
• Do not manually remove hard-bounced addresses from the suppression list or re-import invalid emails.
• Use double opt-in and validate email addresses before importing large lists.
• Remove subscribers who have been inactive for six months or more to maintain list hygiene.
• Allow automatic retries for soft bounces and monitor repeated failures, especially at the domain level.
• Sync bounce data with your CRM using webhooks to automate updates and internal notifications.

Common Bounce Scenarios

• A typo in an email address usually results in a hard bounce (550 5.1.1) and is automatically suppressed.
• A full mailbox typically causes a soft bounce (452 4.2.2), which is retried and suppressed only after repeated failures.
• A non-existent domain leads to a hard bounce (553 5.3.0) and automatic suppression.
• Spam filter rejections often appear as soft bounces (550 5.7.1) and may require content or reputation improvements.

Frequently Asked Questions

1.Do bounced emails count against my sending limit?

Yes. They were attempted deliveries and consumed system resources.

2. Can I remove an address from bounce suppression?

Yes, via API, but it is strongly discouraged. Hard-bounced addresses will bounce again.

3. How long are soft bounces retried?

• First retry: 4 hours

• Second retry: 24 hours

• Suppressed after 3–5 consecutive soft bounces

4. What’s the difference between a bounce and a block?

• Bounce: Receiving server rejects the email

• Block: Email is prevented from being sent (suppression, paused domain, etc.)

5. How accurate is bounce classification?

• Hard bounces: 95%+ accuracy

• Soft bounces: 90%+ accuracy

Based on standard SMTP error code interpretation.

Bounce handling in MailerLogic is fully automated, helping protect your sender reputation and keep your contact database clean. By detecting failures, classifying them accurately, suppressing invalid addresses, and providing detailed reporting and webhooks, it ensures better deliverability, reduced waste, cleaner data, and reliable analytics. Monitoring your bounce rate and following best practices will help maintain strong inbox placement.