> For the complete documentation index, see [llms.txt](https://docs.sendwithses.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.sendwithses.com/faqs/sms-faqs/sms-deliverability.md). # SMS Deliverability SMS's are of two types. When triggering an SMS you must mention the type. 1. ***Promotional*** – Noncritical messages, such as marketing messages. Most Promotional SMS's are delivered but a few can be undelivered - usually because your messages have been blocked by the end user or by the telecom provider. 2. ***Transactional*** – Critical messages that support customer transactions, such as one-time passcodes (OTP). Transactional SMS's are almost always delivered All countries and telecom providers within those countries place numerous restrictions, especially on Promotional SMS. For example, you cannot send Promotional SMS to Indian mobile numbers during 9PM - 9AM. **DO NOT ever make the mistake of sending Promotional SMS's under the Transactional route.** Newbies always assume they can get away with this practice. Mobile phone users tend to have a very low tolerance for unsolicited SMS messages. Response rates for unsolicited SMS campaigns will almost always be low, and therefore the return on your investment will be poor. **REMEMBER**: You are billed for SMS's even if they are undelivered. Additionally, mobile phone carriers continuously audit bulk SMS senders. They throttle or block messages from numbers that they determine to be sending unsolicited messages. **Once you get on the block list, it is impossible for you to get out.** ### Read More: [SMS Best Practices](https://docs.aws.amazon.com/pinpoint/latest/userguide/channels-sms-best-practices.html). --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://docs.sendwithses.com/faqs/sms-faqs/sms-deliverability.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.