Block Non US SMS Messages

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Vijay Kalagara
New member
Username: Vkalagara

Post Number: 1
Registered: 08-2014
Posted on Wednesday, August 13, 2014 - 11:56 am:   


We are looking into NowSMS product for sending 2-way messages and we would like to know if we can block responding to SMS messages coming from outside of US to avoid text message charges. Do you have a solution/config setting for this?

Des - NowSMS Support
Board Administrator
Username: Desosms

Post Number: 4994
Registered: 08-2008
Posted on Wednesday, August 13, 2014 - 12:40 pm:   

Hi Vijay,

The best way to handle this is to include the logic to test the sender in your 2-way command.

However, it is also possible to configure the outbound SMSC connection to limit what addresses it can send to.

If "Support any outbound message traffic"is enabled for a connection, then that connection can send to any destination.

For a typical US-only configuration, it would depend on what format the inbound messages arrive in...specifically what the sender address format is. Ideally, it would be in international format already, e.g., start with +1. If this is the format you are seeing, then, uncheck the "Support any", and add +1* to the preferred list. This means the modem can only send to numbers that start with +1.

If this is your only connection, or no other connections have "support any", then messages to other destinations will error out and fail.

On modems with some US operators the sender address is not in international format. International numbers are prefixed with 011 instead of + (or 00 instead of + in other countries). In this case, you could add all of the following to the the preferred list:


International destinations other than +1 would fail, as would 011 or 00 international prefixes.

There are also configuration settings that can be applied to automatically convert numbers to international format where necessary. See this article for details:

Unfortunately, there are other countries than the US in country code 1, such as Canada and some Caribbean islands. So if you need to block those, it gets more complicated. Blocks can also be used in the preferred list, for example Trinidad and Tobago is in country code 1 with the 868 area code. Blocking all variations of it from a route involves adding block entries to the preferred list. Block entries start with !, as shown in this example:


If you have to deal with area codes like this, it becomes very complicated, and a better solution would be to ask the provider to disable the ability to send messages to international destinations.

NowSMS Support
Vijay Kalagara
New member
Username: Vkalagara

Post Number: 2
Registered: 08-2014
Posted on Wednesday, August 13, 2014 - 12:44 pm:   

Great response with all details!!


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