When you receive a Transmittal you can see it in both Workflow Inbox or Transmittal Log.
In the particular case of transmittals, it is a one-way communication, as such, once you received this document you can just accept it and the communication will finish at this point.
As seen in the Transmittal Workflow section, the document is finally accepted once reaching the destination, finishing the workflow as shown below:
Now the workflow has been completed and therefore the document will appear filtered as 'Sent/Received'. If you open the Cover Sheet, you can see it has been received as well with the 'Receipt Confirmed' mark:
