What is Rate Limiting?
Rate limiting is a technique that restricts the number of API requests or emails a sender can make within a specific time window, protecting systems from abuse and ensuring fair resource usage.
Rate limiting controls how frequently actions can be performed—whether API calls, email sends, or login attempts. It's a fundamental protection mechanism used throughout email infrastructure.
API rate limiting restricts how many requests you can make to an email service. Exceed the limit and you'll receive error responses (usually HTTP 429 "Too Many Requests"). Limits might be per second, per minute, or per day, often with burst allowances for short spikes.
Email rate limiting restricts how many messages can be sent. This happens at multiple levels: your email provider may limit total sends per day, receiving servers limit accepts per sender, and individual mailbox providers limit per-recipient frequency.
Why Rate Limiting Matters
Rate limits are the guardrails of email infrastructure. Hit them, and your sends fail or queue indefinitely. Understanding the rate limits at each stage—your provider's API, receiving servers, individual mailboxes—helps you architect systems that send reliably without hitting walls. For transactional email, exceeding limits means critical messages don't get sent.
How Ark Handles Rate Limiting
Ark's API rate limits are generous and clearly documented. We provide rate limit headers in every response so you can track your usage. Our batch endpoints let you send up to 100 emails per request, reducing API calls while maintaining deliverability. If you need higher limits, contact us—we work with high-volume senders to ensure their critical messages flow smoothly.
Frequently Asked Questions
What happens when I hit a rate limit?
You'll receive an error response (HTTP 429 for APIs). The response usually includes a 'Retry-After' header telling you when to try again. Properly designed systems catch these errors and implement exponential backoff.
How do I avoid hitting rate limits?
Use batch endpoints when possible, implement queuing on your side to smooth out spikes, respect Retry-After headers, and use exponential backoff on errors. For consistent high volume, talk to your provider about increased limits.
Are rate limits the same for all email providers?
No, they vary significantly. Gmail, Yahoo, and Microsoft all have different limits, and they adjust dynamically based on your sender reputation. New senders face stricter limits that relax as reputation builds.
What's the difference between API rate limits and sending rate limits?
API rate limits control how fast you can call the email service. Sending rate limits control how fast emails actually go out to recipients. You might make API calls faster than emails are sent if your provider queues internally.
Related Terms
Email Throttling
Email throttling is the practice of limiting the rate at which emails are sent or accepted, used by ...
Email API
An email API (Application Programming Interface) allows developers to send, receive, and manage emai...
Email Deliverability
Email deliverability is the ability to successfully deliver emails to recipients' inboxes rather tha...
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