It depends what the cover letter is accompanying. In most all cases it should be a business type letter and formatted as such.
If the cover letter is accompanying a resume or job application keep it short and to the point: Attached or enclosed please find my, insert appropriate item,. I look forward o an in person meeting at your convenience. Sincerely.
If you know anything about the company you are applying to you can add in that you have heard wonderful things about them and what they do and how you feel you will be an asset to them. Remember to keep it short. In this case less is more as whoever is reviewing applications will be reviewing many and the less that has to be read the better. The same is true about resume. Short and to the point. You do not need to give a life history just enough to get an interview.
Other cover letters are handled in the same manner. Make your point as fast and with the fewest words as possible. Thank them for taking the time to look at what you have sent. Always say you look forward to hearing from them, meeting them or receiving them. Make sure contact information is available in either your header or after your salutation.
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