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, 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 event is received twice.
During this verification window, your automation can check logs or existing records for matching events and halt any duplicate sends.
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.
4. Centralize automation control
Duplicate sends often originate from fragmented systems where multiple platforms react independently. If your CRM, form builder, and email 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.
