This topic describes the limitations of Alibaba Cloud Short Message Service (SMS), such as message sending frequency and SMS length.
SMS character limit
A message supports up to 1,500 characters. However, a single SMS message that contains more than 160 characters, or 70 if the message contains one or more Unicode characters (such as emoji or Chinese characters), is split into smaller messages for transmission.
- GSM-7 Encoding
When you send an SMS message containing more than 160 characters, the message is split into smaller messages for transmission. These smaller messages are known as "segments" and consist of up to 153 characters each. A data header is included with each segment to ensure proper reassembly by the device of the recipient, reducing the effective character limit per segment to 153.
While message concatenation allows you to send longer SMS messages, it also increases the cost per message, as SMS messaging is billed per segment.
Example: If a message contains 350 characters, it is split into three messages. The first two messages contain 153 characters each and the last message contains 44 characters.
- UCS-2 Encoding
SMS messages are typically encoded using the GSM-7 character set, which supports standard Latin characters and a limited set of special characters. However, if you include non-GSM-7 characters, such as Chinese script or emoji, in your SMS messages, they will need to be sent using the UCS-2 encoding.
Messages that contain one or more UCS-2 characters can contain up to 70 characters in a single, non-segmented message. If the message exceeds 70 characters, it will be split into multiple segments, with each segment containing up to 67 characters.
Example: If a message contains 160 characters, it is split into three messages. The first two messages contain 67 characters each and the last message contains 26 characters.
Message sending limit
To help prevent abuse of the SMS service and protect recipients from spam, Alibaba Cloud allows you to configure the daily delivery frequency of messages to an individual mobile number. By default, the maximum number of messages that can be sent to a single mobile phone number per day is 20.
For more information, see Set the sending frequency of text messages.