Mailslicer: API Documentation

General Information

The Mailslicer API provides access to supported platform features through a personal API key associated with your account. API access must be enabled before any requests can be made.

When API access is enabled, a secret API key is generated for your account. This key is required to authenticate requests and should always be handled as confidential account credentials.

Enable API access

Open the API section in your account and click Enable API. Once enabled, an API key will be generated for your account and displayed in masked form.

Copy your key

Use the Copy API key button to copy your key for use in your application or backend environment. This makes it easier to transfer the key without displaying the full value unnecessarily in the interface.

Rotate your key

Use Rotate when you want to replace the current key. Rotating generates a new key and invalidates the previous one, so all existing integrations must be updated accordingly.

Your API key should be treated like a password. Store it securely and rotate it immediately if you believe it has been exposed.

Authentication

To authenticate a request, include your personal API key in the x-api-key request header. This header is required for all supported Mailslicer API endpoints.

The API key is generated in your account after API access is enabled. Only the currently active key can be used. If the key is missing, invalid, or outdated, the request will be rejected.

x-api-key: your_api_key_here

Store your API key securely and use it only in trusted environments. After rotating the key, update all integrations to use the new value.

Integrations

Below are the integrations currently available through the Mailslicer API.

Email Validation

The Email Validation integration validates a single email address and returns a score based on the verification result.

Request details

Send a POST request to the following URL using a JSON body. Include your API key in the x-api-key request header.

https://app.mailslicer.io/api/email-validation

POST https://app.mailslicer.io/api/email-validation
Content-Type: application/json
x-api-key: your_api_key_here

{
  "email": "[email protected]"
}

curl --request POST 'https://app.mailslicer.io/api/email-validation' \
  --header 'Content-Type: application/json' \
  --header 'x-api-key: your_api_key_here' \
  --data '{
    "email": "[email protected]"
  }'

Each request to this endpoint consumes 1 credit. In API usage history, this request appears with the action Email Validation.

Successful response

A successful response returns the submitted email and its validation score.

{
  "email": "[email protected]",
  "score": 50
}

Possible email scores

99 - single exact match
95 - multiple exact matches
60 - single possible valid email
50 - multiple possible valid emails or catch-all domain
0 - no valid result

Credits & History

Supported API requests consume account credits and create usage records in your account history.

The exact number of credits used and the history entry details depend on the integration being called. These details are described in each integration section of this documentation.

Review your account history to monitor API activity and associated credit usage.

Errors

If a request cannot be processed, the API returns an error response. Current integrations may return the following status codes.

400 Bad Request

Returned when the request body is missing required fields or contains invalid data.

401 Unauthorized

Returned when the x-api-key header is missing, invalid, or unauthorized.

402 Insufficient credits

Returned when the account does not have enough available credits to process the request.

500 Internal Server Error

Returned when an unexpected server-side error prevents the request from being completed.

Integration-specific request validation and response examples are described in the corresponding integration sections of this documentation.