Sending a resume without a cover letter is something akin to sending a boat onto the water without a rudder. There is no clear way forward.
Firstly the recipient has to make assumptions about the purpose of the resume and if the objective does not clearly state your intentions the resume very quickly reposes at the bottom of the bin.
Sending a resume without a cover letter is a killer mistake. It automatically ensures that your application goes no further than an acknowledgement of receipt.
As we have already detailed a well-written cover letter is a most effective tool in your job hunt. Your cover letter begins the job that your resume is going to finish, securing the interview you have been seeking.
Most recruiters divide cover letters and resumes into three distinct piles; probables, possibles and rejects. Decide now which pile are you going to be in?
To ensure that you make it into the probables pile you must create a targeted, professional cover letter that ensures your resume is given the attention it deserves.
To even make it into the possibles you must create a cover letter designed around the needs and expectations of the recruiter. You have to spell out exactly what it is that you intend to do for them and how employing you is going to change their fortunes.