Remember, you're hoping the person who receives your letter has no memory of your closing at all. The last thing you want is a hiring manager going into an HR meeting with your cover letter in hand, asking the team if they want to meet with "Mr. Kindest Personal Regards."
Quick Tip: Don't use your work email address for job searching. Use your personal email account, or set up a unique account to use just for your job hunt. Many free online email services exist, like Gmail and Yahoo mail, that you can use to set up a new email account exclusively for your job search.