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]
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The American Heritage® Idioms Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.