In reporting you will see a status option. This shows the sending status as either Preparation, Sending, Resending, Stopped or Finished.
Preparation (yellow) means it is preparing to send your message.
Sending (green) means it is currently sending.
Resending (light blue) means it has finished the initial send try and will continue to resend until it the optimal delivery has been made.
Stopped (red) means it has been stopped by you using the Stop Delivery option under Reports.
Finished (gray) means the message has been sent and is no longer retrying to send. Reports will continue to update as subscribers show activity on the delivered messages.