What is rate limiting per account or token?
Still have a question, spotted an error, or have a better explanation or a source we should cite?
You're building out your integration with a new ESP, everything looks good, and then suddenly your API calls start returning errors. No warning, no obvious reason. There's a decent chance you've just hit a rate limit.
Rate limiting is how ESPs control how many emails an account or API token can send within a given time window. Think of it as a speed governor. It's not there to make your life harder. It's there to protect shared infrastructure from being overwhelmed by any single sender, whether that sender is a legitimate business having a big launch day or an account that's just been taken over by someone with bad intentions.
Most ESPs set limits at a few different levels. New accounts typically start low (somewhere around 1,000 to 10,000 emails per day) while the platform builds trust in your sending behaviour. Established accounts get higher limits based on their history. Enterprise accounts usually negotiate custom limits upfront in their contract.
API tokens often have their own separate limits on top of your account-level cap. For transactional sending, you might hit per-second or per-minute burst limits even if you're well within your daily allowance. This is especially common with providers like Postmark or Twilio SendGrid, which treat burst control seriously to protect their shared IP pools.
Still when you exceed a limit, the ESP will either reject the request outright, queue it for later delivery, or pause your account until the window resets. None of those feel great, but rejection and queuing are far better than the alternative of letting a compromised account send millions of spam messages before anyone notices.
Rate limits also protect your own reputation. A sudden sending spike (even from you, even intentional) can look like abuse to inbox providers and hurt your sender reputation before you've had a chance to explain yourself.
If you're legitimately hitting your limits, it's usually a quick fix. Contact your ESP, explain your sending needs, and share some context about what you're sending and to whom. Most platforms will increase limits for senders with a clean history. (The key phrase there is clean history. Good engagement, low bounces, low complaints.)
Not sure whether your current setup is optimised for high-volume sending? We're happy to take a look. Drop us a message on the SOS hotline and we'll give you an honest read on where you stand.
Contributors
Who worked on this answer
Every name links to their profile. Every company links to their site. Real people, real accountability.
