In ACE Agent Accept or F10 opens the Received mail support function. In a client setting you can specify that emails are accepted automatically.
The accepted mail is seen as to the left in the screen shot below.
Attachments are seen by the clip 
.
Open or save the file via the right click context menu.
To write a reply to the mail, open Mail reply with Ctrl Alt R or the Reply button.
In a client setting you can specify that Mail reply shall be opened automatically.
Enter your text and right-click for spell-check etc.
To send the mail and close Mail reply use Ctrl Alt S or the Send button.
To terminate the email contact and close Received mail, click on Close button in the main window. In a client setting you can specify that Received mail is closed when you send the reply.