To Whom It May Concern,
To Whom It May Concern is known as a salutation in a letter or poster, by which the writer wishes to exclude the gender of the reader from the salutation and/or to convey that the reader should forward the copy to one more suited to receive or respond appropriately. A comma follows the salutation and name, while a colon is used in place of a comma only in business correspondence. This rule applies regardless of the level of formality of the correspondence.
It is applicable to several kinds of letter templates, such as a Letter Of Resignation, Notarized Letter of Employment, Job Vacancy Description, Recommendation Letter, Press release, etc.