It is always considered best practice to go into the Sent Log and review whether the message appears in the Report. If so, this means that the system was able to generate the message and there is nothing more that needs to be done.

If your message left our system and is in the sent log with a N/A delivery status, this means that the message has been sent upstream but the DLR (delivery report) has not been received.  

Once a message leaves our system it is sent to an Aggregator who then sends the message to your Carrier. From there, the Carrier is responsible to send it to the local cell tower then your handset. At any point, there can be an issue that can delay or prevent a message from being delivered. 

Or perhaps you have opted out of receiving messages? If the opt-out was on a SHORT-CODE - text the KEYWORD back to the short-code. If the opt-out was on a 10-DLC or TOLL-FREE # - reply UNSTOP to the messaging code. Otherwise, please proceed to the article below

See Related Article: Problems receiving SMS or MMS messages on cellphones?