Cover letter writing concept has been changed, as many Top and lower class of companies are scanning Cvs, emails and cover letter too to get instantly result what they want to look. I would say if we include job related keywords in our resume so that it helps to get it scan easily which not only help to get instant response but also help to get instant result of your cv. The perfect Cover letter is one which is written by keeping in mind job requirement with enough keywords that matches the job requirement and help to get it scan easily.