Cover letter is the accompanying document of a resume for each job application. Thus, it is a prerequisite to check where you are going wrong in drafting the cover letter if you are not getting response from the recruiters. Checking the resume is the first step and then refer to the job description given by the employer. Have you written it according to their necessities?
If yes, then the next thing is to check for other mistakes as described below.

Follow Up:
The first thing while trying to gauge why you are not getting response from a recruiter is to follow up with them. Quote the date when you had submitted your resume and inquire if they have gone through the resume. You never know if the resume is misplaced or mishandled.
Customize:
Every cover should be personalized with not just the recipient's name, but also with your own reasons for taking a decision to apply in that firm. It is imperative to avoid any kind of loopholes in the resume, because it might turn out to be a blunder in the recruiter's eye. Mistakes in cover letters translate into insincerity and callousness which are not good for your candidature.
Proofread:
Spelling mistakes are the most common errors in cover letters as reported by some surveys of the recruiters. It puts off the reader when they see that the candidate has not taken enough care to go through what they have written. Or else, it also translates into something like the candidate is bad at the language basics.
Contact Details:
Make sure the contact details given in your cover letter for resume is accurate, especially so in case of phone numbers along with codes and the e-mail addresses. You never know with the automatic changes running on the computers. Some spellings might have auto corrected itself and the address turns out to be wrong.
Contact Person:
In case you have addressed the letter to a particular person, (as per rule) then ensure by inquiring that the letter has reached the recipient. If the person is on leave, has been transferred or has resigned, etc., in such cases the personally addressed letters are not entertained by anyone.

These were the main factors where a candidate's cover letter goes unnoticed. These check points will surely help you to make out where your cover letter is lacking. Circumstances can be any, so never assume things or take it for granted either. When it comes to a job, you might as well be sure than leaving things to fate.
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