When it's your turn to handle an ACD Email or Fax interaction, you will get a pop up notification regarding the inbound interaction.
Press the green button to accept or the red button to reject the interaction.
Alternatively , you can accept or reject the interaction from the Inbox as seen below.
Notice the Red Circle in the left panel indicating the inbound offering.
Press the blue circle with the check mark in it to accept it and reply or the blue circle with the X in it to reject.
Once accepted, you can work with it:
Enter your reply, then press the blue circle with the paper airplane in it to send.
If you would like to check to see if this person has any historical Email interactions, you can click on the blue circle with the timer in it, then click on "Customer".