Best Regards

A valediction (derivation from Latin vale dicere, "to say farewell"), or complimentary close in American English, is an expression used to say farewell, especially a word or phrase used to end a letter or message, or the act of saying parting words whether brief or extensive.

Its greeting counterpart is called a salutation.

The term is also used to refer to the speech given by a valedictorian at a commencement and to refer to final prayers and remarks at the graveside before a burial.

Valedictions normally immediately precede the signature in written correspondence. The word or words used express respect, esteem, or regard for the person to whom the correspondence is directed, and the exact form used depends on a number of factors

In British English, valedictions have largely been replaced by the use of "Yours sincerely" or "Yours faithfully". "Yours sincerely" is typically employed in English when the recipient is addressed by name (e.g. "Dear John") and is known to the sender to some degree, whereas "Yours faithfully" is used when the recipient is not addressed by name (i.e. the recipient is addressed by a phrase such as "Dear Sir/Madam") or when the recipient is not known personally by the sender.

The following table contains complimentary closings as recommended for business hard-letter use by two American authorities: Barron's Educational Series and American Management Association.

Valedictions in formal e-mail are similar to valedictions in letters; on the whole, they are variations of "regards" and "yours". However, a wide range of popular valedictions are used in casual e-mail but very rarely in letters.

Current regulations of the United States Department of Defense, the Joint Chiefs of Staff, the U.S. Air Force, the U.S. Army, and the U.S. Navy call for two complimentary closings for letters: "Respectfully yours" and "Sincerely". "Respectfully yours" is reserved for the President, except the Army includes the President's spouse, and for the President-elect. "Sincerely" is used in all other cases.

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Wikipedia