To pin down the case let´s put two examples of big companies: Amazon and Google. They both have job offers posted online but they proabably receive thousands of applications daily.

I imagine that there are some preliminary, automated filters to avoid reading all of them. I guess they probably look for certain key words, or something similar. I am just wondering here, and would appreciate the confirmation of someone with experience as a recruiter on a company like this.

My point is, even if I have a decent curriculum, is it a waste of time to simply send it along with a cover letter for the position offered without any inside contact on the company? If it is not, which is the best way to ensure your resume+cover letter arrive to the hands of someone capable to understand your technical accomplishments rather than simply an HR agent?