Notes and Constraints

SMN pushes messages asynchronously, which does not ensure the timeliness of message delivery. If your service requires messages need to be delivered in a quasi-real-time manner, exercise caution whether to use SMN.

The email addresses and phone numbers for receiving emails or SMS messages or voice calls from SMN can be changed. Do not whitelist such email addresses or phone numbers. Otherwise, SMN messages may fail to be received if they are changed.

The source IP address used by SMN to send messages is not fixed and may be changed at any time. Do not configure a whitelist for source IP addresses, or you may fail to receive SMN messages.

For network security purposes, SMN does not send messages to Huawei Cloud private networks by default.

SMN imposes restrictions on some items. Do not exceed their limits when using SMN. Otherwise, program exceptions may occur.

Table 1 lists the restrictions on topics.

**Table 1** Restrictions on topics
Item	Quota	Description
Topic name	1 to 255 characters	If you enter 256 or more characters, the topic cannot be created.
Display name	192 bytes	If you enter 193 or more bytes, the topic cannot be created.
Tag	20	If you add 21 or more tags to a topic, the topic cannot be created.
Tag key length	128 characters	If you enter 129 or more characters, the tag cannot be created.
Tag value length	256 characters	If you enter 257 or more characters, the tag cannot be created.
Text message title	512 bytes	None
Text message content	256 KB	If a message exceeds 1,000 characters, the message delivery will fail due to message length limit by carriers.
JSON message content	256 KB	None
Template message content	256 KB	None

Table 2 lists restrictions on subscriptions.

**Table 2** Restrictions on subscriptions
Item	Quota	Description
Endpoint	10,000	None
Validity of a subscription confirmation link	48 hours	Confirm the subscription on your mobile phone, mailbox, or other endpoints in time.