Did you actually try it?

I realise that Body may be described as an attribute in the OLE documentation for Outlook, but the error message certainly imples that it ends up being implemented as a method within Win32::OLE.

The error message is pretty indicative.

{ 
    my $s = 'the quick brown fox'; 
    sub Body{ 
        ($s) = @_ if @_; 
        $s 
   } 
}
print Body();

the quick brown fox

Body = 'fred';
Can't modify non-lvalue subroutine call in scalar assignment at (eval 
+3) line 1, at EOF

Body( 'fred' );
print Body();

fred
[download]

If you did try it, what error message did you get from the attempt?

Hmm, it seems if you try it as Body($mybody) instead of {'Body'} = $mybody you get an error "Invalid number of parameters" from Win32::OLE. For what it's worth, http://perlmonks.thepen.com/185757.html seems to think the {'Body'} method is correct.