Throttling
What is Throttling?
Throttling is when an API or messaging platform deliberately slows or rejects requests once a sender passes its allowed rate — returning an HTTP 429 'too many requests' response on an API, or holding excess messages in a queue instead of delivering them immediately. It protects the platform and downstream carriers from a burst that would degrade service for everyone, and unlike rate limiting, throttling usually queues excess traffic for later delivery rather than rejecting it outright.
More detail
Throttling and rate limiting are related but distinct controls: a rate limit rejects traffic over the cap immediately (an API returns 429, or a messaging gateway refuses the send), while throttling typically queues the excess and drains it at the allowed rate, so a burst campaign arrives delayed rather than dropped.
In messaging, throttling is what enforces a channel's assigned throughput — Messages per Second. Sustained overages can still trigger carrier filtering or failed deliveries, so senders throttle their own send rate proactively instead of relying on the platform's queue to absorb every burst.
On the API side, a well-behaved client handles throttling with retry-after semantics: read the retry hint in the 429 response, back off, and resume at the allowed rate rather than hammering the endpoint with immediate retries.
Frequently asked
- What is the difference between throttling and rate limiting?
- Rate limiting rejects requests over the cap immediately — an API returns HTTP 429 or a messaging gateway refuses the send. Throttling usually queues the excess and drains it at the allowed rate, so the traffic is delayed rather than dropped. The two often sit side by side in a platform's limits.
- What should I do when I receive a 429 too-many-requests response?
- Back off and retry at the allowed rate, honoring any retry hint the response carries, instead of retrying immediately. Sustained 429s mean the sustained send rate needs to come down, not that retries are misconfigured.
- Does throttling mean my messages were lost?
- Usually no — throttled messages sit in a queue and drain at the allowed rate, so a burst campaign is more likely to arrive delayed than dropped. Messages only fail if the queue overflows or a sustained overage triggers carrier filtering.
See also
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