Your delivery status comes directly from the networks, here we've got an explanation for the most common delivery statuses:
Your message has successfully been delivered to the handset.
Sent to Network / Pending with Network
Your message has been sent to the mobile network, but the network has not successfully reached the handset as of yet. This is likely due to the recipient's mobile being out of signal or turned off etc. The networks will continually retry over a period of up to 72 hours to deliver the message.
The networks have been unable to deliver your message to the handset. If a message is declined instantly by the network, this usually indicates that the number is no longer active / not recognised and we recommend cleansing your database of these numbers.
Occasionally, you may see additional statuses returned by the networks:
The message is currently being submitted through the networks, but is currently not been processed. This is most likely due to a congestion or an issue with the network of the recipient.
The message has been rejected by the network or the handset. There are many reasons for this, the most common is due to the handset not able to support SMS - either because their handset is out of memory, or the device is not a standard mobile phone.