You can get the contents of a selected message with
tell application "Mail"
set myMessage to first item of (get selection)
set myContent to content of myMessage
end tell
How do you get the contents of a message which has been opened in its own window?
It’s always better to ensure that the process is a frontmost process. Thus, even if “Male” is not already running, but in the previous session you had a message selected, everything will work (as the “Mail” remembers its last selection):
tell application "Mail"
activate
set myMessage to first item of (get selection)
set myContent to content of myMessage
end tell