SMS and Spam filtering: TopView delivers SMS successfully but message does not reach recipient

TopView can send SMS notifications through Email-to-SMS or via a networked cellular modem.

Sometimes, SMS messages are not received by the notification recipient even though TopView reports the message as correctly delivered to the carrier's email-to-text gateway (via Email-to-SMS) or the cellular modem.

Carrier spam filtering is usually the cause of undelivered messages

Usually, this inability to deliver the message is a result of spam filtering by the carrier. Carrier's in the US, and in many other countries, are required by law to recognize and filter spam to prevent nuisance text messages.

Because TopView messages can be delivered in bulk and may contain similar text across messages, they can look a lot like spam to carriers.

Consider the following mitigations:

1. Send fewer notification messages
   
2. Adjust alarms messages to be different from one another
   
3. Add delays in notification groups to increase the time between the SMS message notifications
   
4. Explore options with your carrier. You may be able to purchase a short code, or a different account that will alleviate spam filtering issues. Note: these can be expensive.

Twilio provides a number excellent resources:

1. Twilio Regulatory Guidelines for SMS: a list of regulatory guidelines by country
   
2. SMS Carrier Filtering in the United States and Canada – Twilio Support: Explanation of spam filtering by carriers in the US and Canada.

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