Knowledge base

Rate limits: How to reduce 403, 422, & 429 errors

If you've encountered 403, 422, or 429 errors while using MailerSend's API, it's important to understand what these errors indicate, as well as the rate limits and quotas associated with your plan.

Daily Request Quotas

MailerSend has a daily request quota for API and SMTP relay services which varies depending on your subscription plan. Every request made counts against your daily quota, which is reset daily at midnight UTC.Premium

Plan Quota / day
No Plan 100
Free 1000
Premium 100,000
Enterprise 500,000

What happens when you exceed your quota?

When you hit your daily quota, you will start receiving a 429 HTTP error. Two HTTP headers will be returned with every API request to indicate the quota limit and when the quota will be reset.

Rate limit errors

429 - Too many requests

What it means: You've exceeded your rate limit or daily quota.

Types of rate limits:

  • Rate limit per minute: This type of rate limit caps the number of API requests that can be made per minute.

  • Daily quota: This is a longer-term limit on how many API requests you can make in a 24-hour period.

For each MailerSend plan level, there are rate limits specified for different types of requests:

Endpoint Healthy reputation Under review reputation
All API requests (excluding v1/email) 60 requests per minute 60 requests per minute
API requests to v1/email 120 requests per minute* 10 requests per minute
API requests to v1/bulk 10 requests per minute 1 request per minute

*Newly upgraded accounts may have a lower rate limit until they've been established as a sender with good sending practices.

422 - Validation errors

What it means: This error means a validation error was found when processing your request.

How to reduce validation errors:

  • Ensure your API requests are formatted correctly and all required parameters have been included

  • Refer to MailerSend's developer documentation for sample code and guidelines

  • If you're using MailerSend templates, ensure that you're following the correct template structure

403 - Forbidden errors

What it means: A 403 Forbidden error indicates that you're trying to access a resource on the server that you're not authorized to access. Unlike 401 Unauthorized errors, where authentication might solve the problem, a 403 Forbidden error signifies that authentication won't help. Your credentials may be valid, but you still don't have permission for a specific request.

Common scenarios

  • Invalid API Key: If the API key you're using is invalid, expired, or revoked, you might encounter a 403 error

  • Insufficient permissions: Your API key might be valid but lacking the necessary permissions to perform a specific operation

  • Account status: If your MailerSend account is suspended, under review, or otherwise restricted, API calls may result in 403 errors

  • IP blocking: If requests are coming from an IP address that has been blocked due to suspicious activity, you might get a 403 error

How to reduce 403 errors

  • Check API Key: Make sure that your API key is correct, active, and not expired

  • Review permissions: Ensure your API key or user account has the permissions necessary for the action you're trying to perform. You may need to generate a new key with broader permissions

  • Check account status: Make sure your account is active and in good standing

  • Examine IP Address: Confirm your IP address is not on any blocklists

  • Check Endpoint URLs: Make sure you're requesting an existing endpoint and that the URL is spelled correctly

  • Consult documentation: Always refer to MailerSend’s API documentation to ensure you're making requests correctly