What is Email Throttling?
Email throttling is the practice of limiting the rate at which emails are sent or accepted, used by both senders to warm up IPs and by receivers to protect against spam floods.
Email throttling controls the rate of email transmission. It works in two directions: senders throttle outbound messages to avoid overwhelming recipient servers or triggering spam filters, and receivers throttle inbound messages to protect their infrastructure from spam attacks or accidental floods.
Sender-side throttling involves limiting how many emails you send per hour, minute, or second. This is essential during IP warmup, when sending to new domains, or when ramping up volume. Sending too fast can trigger rate limits, deferrals, or blocks.
Receiver-side throttling is when email providers limit how many messages they'll accept from you in a given timeframe. If you exceed their thresholds, your messages get deferred (temporarily rejected) with messages like "please try again later."
Why Email Throttling Matters
Throttling directly affects whether your emails get delivered. Send too fast, and you'll hit receiver limits—your messages get deferred, delivery slows to a crawl, and your queue backs up. For transactional email, this means users waiting longer for password resets or confirmations. Understanding throttling helps you plan sending patterns that maximize delivery speed without triggering protective limits.
How Ark Handles Email Throttling
Ark handles throttling intelligently. Our infrastructure automatically adjusts sending rates based on real-time feedback from receiving servers. When a provider starts deferring messages, we back off and retry at appropriate intervals. This happens transparently—you send via API, and we handle the delivery optimization. For dedicated IPs, we provide warmup scheduling guidance to avoid throttling during ramp-up.
Frequently Asked Questions
What's the difference between throttling and rate limiting?
Throttling typically refers to slowing down transmission rates over time, while rate limiting sets hard caps on requests per time period. In practice, they're often used interchangeably. The key distinction: throttling implies graduated slowdown, rate limiting implies binary allow/deny.
How do I know if my emails are being throttled?
Look for deferral messages in your bounce logs—responses like '421 Too many connections' or 'Please try again later.' Also watch for delivery delays that grow over time, or queues that build up faster than they drain.
How fast can I send email without being throttled?
It varies wildly by provider. Gmail might accept thousands per minute from established senders but throttle new senders heavily. Start conservatively (hundreds per hour for new IPs) and increase gradually based on acceptance rates.
Does throttling affect transactional email differently than marketing?
Transactional emails are more time-sensitive—a password reset delayed by throttling is a worse experience than a newsletter delayed. This is why dedicated transactional infrastructure with proper reputation is critical.
Related Terms
Rate Limiting
Rate limiting is a technique that restricts the number of API requests or emails a sender can make w...
IP Warmup
IP warmup is the process of gradually increasing email volume from a new IP address to build sender ...
Email Deliverability
Email deliverability is the ability to successfully deliver emails to recipients' inboxes rather tha...
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