FAQ
Answers to frequently asked questions about message delivery from the international SMS console.
The SMS console shows the message was sent, but it never arrived. How do I fix this?
Start by checking the device:
Restart the destination phone if it has not been rebooted in a long time.
Delete unnecessary messages if the inbox is full.
If the phone has dual SIM slots, swap the SIM cards and try again.
Check whether security software on the phone is blocking SMS messages.
If none of these steps resolve the issue, insert the SIM card into a different phone to determine whether the problem is with the device or the number.
I want to send messages to Vietnam. What message types are supported?
To ensure OTP delivery to Vietnam, messages are automatically converted to text-to-speech calls.
What are the limitations when sending messages to the US, France, and India?
The following restrictions apply:
Promotional messages are prohibited in the US.
Promotional messages are prohibited in France.
How many characters can a message contain?
A message can contain up to 1,500 characters.
What are the rules for setting a daily limit for message delivery?
To protect user experience, no more than a set number of messages can be sent to the same mobile phone number per day. The default limit is 20 messages per day.
Set a custom limit as needed, but the limit cannot exceed 20 messages per day.
A day runs from 00:00:00 to 23:59:59.
Why does ".0" appear after the verification code in an OTP message?
The JSON value for the verification code is a number, not a string. Change the value type to string in your JSON object to remove the ".0" suffix.
Can I send messages to multiple mobile phone numbers at once?
Yes. Send to multiple numbers in a single request by calling an API operation or using the SMS console.
How do I prevent message flooding?
Message flooding occurs when malicious programs send large volumes of messages to many phone numbers in a short time, which can result in recipient harassment and brand damage. Use the following methods to prevent it:
Add CAPTCHAs to your page so malicious programs cannot trigger messages. For example, require a CAPTCHA before sending a verification code.
Set a minimum interval between consecutive verification code requests. A 60-second cooldown is common practice.
Set an expiry period for entering a verification code. Most implementations use 30 seconds — if the code is not entered within that window, it expires and the user must request a new one.
What are the possible causes of message delivery failures?
Number portability: Messages usually follow a number when the carrier changes, but if the new carrier has not updated its routing within 24 hours of the transfer, delivery may fail temporarily.
Device issues: A phone cannot receive messages when its memory is full, when it is in airplane mode, or when it is out of service coverage.
Invalid message content: Messages written in languages or character sets not supported by the destination carrier may fail to deliver.
Roaming: Delivery depends on the roaming interconnection agreements among global carriers, so messages may not reach recipients who are roaming.
Carrier spam filters: Carriers may block messages that contain keywords flagged as spam.
How do I check whether a mobile phone number is valid?
Validate a number against international dialing rules to check its format — this does not confirm whether the number exists, is active, or has changed carriers.
If the number matches the expected format, the message is sent and you are charged by the carrier, even if the number does not exist and the message is not delivered.
Alibaba Cloud SMS can retrieve more detailed number information by querying carrier route databases. This service is typically charged separately.