Through this apple script you can retrieve mail content so please try it.
tell application "System Events"
tell process "Mail"
set _Contents to {}
set _contentDetail to {}
set the _contentDetail to entire contents of UI element 1 of scroll area 3 of window 1
repeat with _value in _contentDetail
set str to ""
if class of _value is static text then
set str to value of _value
end if
set str to str & return
set _Contents to _Contents & str
end repeat
return get _Contents as string
end tell
end tell