to whom it may concern

to whom it may concern

To the person to whom this letter applies or to whom it ultimately reaches. A formal address used at the beginning of a letter or email when the appropriate or ultimate recipient's identity is unknown. To whom it may concern: I am writing today to lodge a formal complaint against your company.
See also: concern, may, whom
Farlex Dictionary of Idioms.

to whom it may concern

Cliché to the person to whom this applies. (A form of address used when you do not know the name of the person who handles the kind of business you are writing about.) The letter started out, "To whom it may concern." When you don't know who to write to, just say, "To whom it may concern."
See also: concern, may, whom
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

to whom it may concern

To the appropriate recipient for this message, as in I didn't know who was responsible for these complaints so I just addressed it "to whom it may concern ." This phrase is a formula used in letters, testimonials, and the like when one does not know the name of the proper person to address. [Second half of 1800s]
See also: concern, may, whom
The American Heritage® Dictionary of Idioms by Christine Ammer.
See also:
  • to whom this may concern
  • Dear John letter
  • a Dear John letter
  • French letter
  • bread-and-butter letter
  • a bread-and-butter letter
  • a dead letter
  • dead letter
  • dash a letter off
  • Xmas