Create a Triggered Send Using the Async API
By using the async API, you can ensure that your call is queued and ready to go once the call is completed, no matter what happens with your network connection. You can also prioritize triggered sends and use the CorrellationID and ConversationID objects to track an exchange of emails related to the triggered send.
Marketing Cloud must enable more functionality on your account so that you can set the priority on a triggered send. Contact your Marketing Cloud representative for more details on this feature and to enable this feature for your account.