Whether to write “To Whom it may concern” or “To Whom it May Concern” is a common question from those who infrequently compose letters of complaint or inquiry. This is a common salutation and so, it is important to get the capitalization right. Indeed, the confusion is quite understandable.
There is a difference in opinion even with leading style guides. The Chicago Manual of Style claims that every word should be capitalized. However, there was no citation or even Q&A entry to back this up. The Gregg Reference Manual addresses this issue in full and led us to our conclusion.
“To Whom it may concern” or “To Whom it May Concern”?
The rule for capitalizations in salutations is that the first word, all nouns and all titles are capitalized. This means that “To whom it may concern” is the correct way to use this salutation. This is the point that is made on the Gregg Reference Manual.
The only words that are capitalized on their own in a salutation are the first word or any proper nouns and words that are standing in for a noun do not upgrade that word to a proper-noun. (This applies to the word “whom” in this case.) If this were the case then we would have to capitalize pronouns such as “he” or “she”. However this is usually only done when referring to a deity and so should not be done in a salutation such as this.
In this way, salutations follow identical capitalization rules as sentences. Although there is some debate as to the right way in which to use the salutation, we conclude that following the guidelines that are set out by the Gregg Reference Manual, “To whom it may concern,” is the correct way in which to use this salutation. Having said this, it should be noted that this is simply an issue of style and so there may not actually be one “correct” way but there is still a standard in general usage.