# How to Avoid Sending Duplicate Emails From One User Action

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## Table of contents

- Why does duplicate email triggering happen?
- How to prevent the triggering of duplicate emails
- Conclusion

Imagine one of your website visitors fills out your form, and instead of receiving a single confirmation email, they get two or even three identical messages. It looks sloppy. Worse, it feels spammy.

If your email workflows are sending multiple emails from a single user action, it directly affects trust, clutters inboxes, and increases the risk of [unsubscribes](https://www.mailmodo.com/guides/unsubscribe-rate/) or [spam complaints](https://www.mailmodo.com/solutions/check-spam-complaints/). Over time, this kind of behavior can also hurt your sender's reputation.

This article explains why duplicate emails happen and exactly how to prevent them with the right logic, safeguards, and automation structure.

## Why does duplicate email triggering happen?

Duplicate email triggering happens when one user action unintentionally activates more automations and more than one email gets sent to the user. These issues usually don’t happen from one major failure, but from a series of small technical gaps, such as:

-   Form submissions are happening more than once due to page lag, refreshes, or double-clicking
    
-   Multiple tools, such as a [CRM and an email platform](https://www.mailmodo.com/guides/crm-email-marketing/), are responding to the same event
    
-   Webhooks or APIs are sending duplicate payloads because of retries or timeout failures
    
-   Missing validation checks to confirm whether an email has already been sent
    

## How to prevent the triggering of duplicate emails

Here is how you can stop your workflows from sending multiple emails for the same user action, using a combination of logic, tracking, and centralized automation.

### 1. Add deduplication logic to your triggers

The first line of defense against duplicate emails is ensuring that your triggers recognize truly unique events. Without this, even a single user action could fire multiple emails if your system receives repeated signals.

Here is how to do it:

-   For unique tokens or IDs: Attach identifiers such as session IDs, submission IDs, or order numbers to every trigger. This allows the automation to differentiate between genuinely new events and repeats.  
      
    
-   For custom events: Structure your workflows to respond only to specific, clearly defined actions. For instance, a “completed purchase” event should fire an email only if it hasn’t been processed before, even if the system receives multiple confirmations.
    

### 2. Add verification steps with delays

Sometimes events appear multiple times due to network lag, webhook retries, or complex workflows. Introducing a short delay, typically one to two minutes, gives your system time to verify that the action is truly new before sending the email.

This is particularly valuable for:

-   Webhook-based triggers: External systems often resend events automatically on failure, which can create duplicates.  
      
    
-   Complex workflows with multiple entry points: When the same user might enter a workflow from different points and activate different triggers, a delay ensures the first event is fully processed before any subsequent one fires.  
      
    
-   Transactional or payment flows: Avoid sending [multiple confirmations or receipts if a payment](https://www.mailmodo.com/solutions/measure-transactional-emails-performance/) event is received twice.
    

During this verification window, your automation can check logs or existing records for matching events and halt any duplicate sends.

### 3. Use tags or properties to track status

Tags and user properties act as internal markers to indicate whether an email has already been sent or a workflow step has been completed. This prevents re-entry and accidental repeats.

Here is how to implement it:

-   Apply tags immediately: When a user enters a workflow or receives a critical email, mark them with a tag such as welcome_email_sent.  
      
    
-   Check user properties: You can also tag users using the contact properties. For instance, a property like email_sent = true can be checked before [triggering any new emails](https://www.mailmodo.com/solutions/email-triggers/).  
      
    

  

### 4. Centralize automation control

Duplicate sends often originate from fragmented systems where multiple platforms react independently. If your CRM, form builder, and [email platform](https://www.mailmodo.com/guides/enterprise-email-marketing-platform/) all trigger emails on their own, overlaps are almost guaranteed.

Centralizing automation in a single platform ensures all workflows respond to one source of truth. This way, you can define precise conditions for when an email should fire, eliminating the risk of accidental duplicate sends across multiple systems.

Platforms like Mailmodo allow you to manage workflows from a single hub, so every trigger is evaluated consistently and redundancies are avoided.

### 5. Monitor and log sends

Visibility is key to preventing and troubleshooting duplicate emails. Maintaining a send log helps you track patterns, identify weak points, and refine your workflows.

A comprehensive log should include:

-   User ID or email address to link sends to individual users.
    
-   Timestamp of the email to track the order and timing of sends.
    
-   Workflow or trigger source to identify which automation caused the email.
    

Over time, these records provide insights into recurring issues, help optimize trigger logic, and ensure your email program is both reliable and professional

## Conclusion

Duplicate emails often surface when workflows evolve or new tools are added. Regular audits of your automation rules can catch gaps before they impact subscribers.

Establishing a routine review process helps maintain a clean, efficient email program, ensuring your campaigns remain effective as your stack grows or changes.

## Frequently Asked Questions

### Are certain types of emails more prone to duplication (transactional vs marketing)?

Transactional emails, such as order confirmations or password resets, are more sensitive because they are often triggered by critical events. Marketing emails can also duplicate, but the impact is mostly engagement-related rather than transactional confusion.

### How can form design help prevent duplicate submissions?

Preventing double submissions can be as simple as disabling the submit button after the first click, showing confirmation messages, or using session tokens to track uniqueness.

### How can user behavior, like double-clicking, trigger multiple emails?

Double-clicking a button or refreshing a page can submit the same form twice, firing the workflow twice. Using unique submission IDs or throttling submissions can prevent this.

### Can A/B testing in workflows accidentally create duplicate emails?

Yes. If both test branches send emails triggered by the same action without proper deduplication, a user could receive multiple messages. Proper tagging or conditional logic can prevent this.

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