--- title: Rate Limits and Message Queues | Sendblue Docs description: API Rate limits | iMessage for Business --- ## Introduction Sendblue has safeguards in place to reduce spam, increase uptime, and comply with Apple’s rate limits. These are: - Account-level quotas - Dynamic rate limits - Sender Pools ## Account-level quotas ### Free plans Free plans are subject to the quotas the we have listed on our [homepage](https://sendblue.com) ### Blue Ocean plans Blue Ocean plans allow for infinite scalability on Sendblue. It is important that we understand your use case to ensure the highest possible deliverability. Please [book a demo](https://sendblue.com/request-a-demo) to find out more information. ## Rate Limits ### Message Throughput Each dedicated number can send up to 1 message per second (industry standard). Additional safeguards may apply depending on your use case and traffic patterns. The rate limits per line differ depending on whether you send the first message to a contact (outbound-initiated) or they send you a message first (inbound-initiated). All limits apply across all messaging channels, including iMessage, SMS and RCS. ### Blue Ocean Limits These limits are based on unique contacts per line and reset daily at 3am EST. | Scenario | Counts Against | Limit | | --------------------------------------------------------- | --------------- | -------------------------- | | You text a contact who has never texted you | Outbound limit | 50 contacts/day/line | | A contact texts you (inbound message) | Inbound limit | Unlimited contacts | | You reply within 24 hours of their last message | No limit | Unlimited messages | | You message first after 24 hours since their last message | Follow-up limit | 200 contacts/day/line | | You are messaging a contact who has not replied | Follow-up limit | 5 messages without a reply | Please reach out to the Sendblue team if you have questions about best practices or how to maximize your response rate. ### AI Agent Plan Limits These limits are based on unique contacts per line in a rolling 24-hour window. | Scenario | Counts Against | Limit | | --------------------------------------------------------- | --------------- | ------------------------- | | A contact texts you (inbound message) | Inbound limit | 1,000 contacts/day/line\* | | You reply within 24 hours of their last message | No limit | Unlimited messages | | You message first after 24 hours since their last message | Follow-up limit | 200 contacts/day/line | \*We recommend load balancing on your end across multiple numbers if you need more capacity. If you cannot control load balancing on your end (billboard campaign for example) the limit can be removed by [texting](sms:+19178379243?body=Hey!%20I'd%20like%20to%20discuss%20upgrading%20to%20the%20blue%20ocean%20plan) or [emailing us](mailto:support@sendblue.com) to upgrade to the Blue Ocean plan. ### How the 24-Hour Window Works The 24-hour window opens when a contact messages you inbound, and it resets each time they message again. While the window is open, you can send unlimited replies to that contact. Once the window expires, messaging that contact first counts against your follow-up limit — until they text you again (which reopens the window). ## Number Pooling In order to send more messages than is possible using a single number, we can pool multiple numbers together to acheive the desired rate. If you need to send 100 messages per second, you will need to have 100 numbers to do so. With number pooling, your business has many numbers that it could potentially send a message from. Although you can send from any of the phone numbers in the pool, each of your recipients by default will only receive messages from the initial number that you use to text them (sticky sending). ## Message Queueing The Sendblue API is designed in such a way that messages will be queued for sending once they reach our API. If you make 10 requests to send 10 messages at second 0, the last message will be sent a the start of second 10. Sendblue will queue all of your mmessages for a window of up to 1, 500 messages, at which point further calls to the API will result in a 429 - “Too Many Requests” response code. As stated before, you are able to send more messages per second when using number pooling. ## FAQ #### Is the rate limit hourly or daily? Both. Message volume limits are enforced on both an hourly basis (default: 2,000/hour) and a daily basis (default: 4,000/day). Conversation-level limits (inbound and outbound) are enforced daily. #### Does using the Lookup API count against message usage? No. Lookups have their own separate rate limits (30 per hour, 100 per day per line by default, up to 400/day upon request) and do not count against your message sending limits. #### What is the 150 consecutive outbound SMS limit? Can it be disabled? Sendblue enforces a limit of 150 consecutive outbound SMS messages per line. This limit cannot be disabled. It exists for line safety and spam prevention — exceeding it risks carrier-level penalties or number deactivation. #### Can we text hundreds of thousands of users? How many lines would that require? Yes, high-volume messaging is supported. The number of lines you need depends on your throughput requirements. Calculate based on the per-line rate limits above (50 new outbound conversations/day, 200 ongoing/day, 1 message/second). For example, to send 10,000 new outbound messages per day, you would need a minimum of 200 lines. Contact your account manager to plan provisioning for high-volume use cases. #### What does “hourly rate limit reached” mean and what should I do? This means you have exceeded the hourly message limit for your account (default: 2,000/hour). To resolve this, either wait until the next hour for the limit to reset, or add more lines to your account to increase overall throughput.