A cover letter is an important part of ones introduction to the company; it is accompanied by a resume and usually stapled on top of the resume. In case of email job applications, the cover letter should preferably be written in the email writing area and resume can be sent as an attachment.
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When one starts looking for a job, there are certain things that have to be kept ready. They may include:
Resume
Cover Letter
Certificates
Individual Photographs
Intimation to references in the resume
Interview preparation according to the job and company in question
In this website, one can find information on "Cover Letter Formats" apart from related articles and useful information.