Whose name should I put in this letter's salutation?

I would say Mr.Johnson as this would address him personally.

If the contact “person” is a single “person,” then just write to him.

Dear Mr. Johnson: Is exactly how it should look, including the colon.

I agree with “Dear Mr Johnson” but not with the colon after the salutation.

I think the colon depends on where you are and the context you are writing in.

A formal letter (which this is) sent via snailmail should have the writer’s full address right-justified at the top, the recipient’s address left-justified and one line below the writer’s address, the salutation left-justified and one line below the recipient’s address (no colon or comma following the salutation), the subject of the letter one line below the salutation (this always begins with “Re:” and is underlined again no punctuation after the last word on the subject line.

At least that’s how you do it if you want to do it right.

@weeveeship Sorry about the digression; you didn’t ask how to format a letter. My original answer still stands. Address it to the person with whom you have contact and don’t follow up the salutation with a colon.

@Rhodentette We were just churning out formal letters in some Business class I’ve been forced to take, and every single salutation ended in a colon. Evidence: “The greeting in a business letter always ends in a colon.”

It’s not like this is an unhelpful digression, though; we’re trying to make his letter that much more correct, after all.

This is an Americanism. If @weeveeship is American or writing to an American, he should use the conventional form of that country, which seems to be to put a colon behind the salutation.

It’s not more or less correct, it’s different.

@Rhodentette Now I understand why there was debate. Thanks for clearing that up.

If you’ve been given a specific contact person, i.e. Mr. Johnson, your letter should be addressed directly to him. In academic situations where there is no specific contact, I’ve always used “Dear Sir or Madam”.

Mr Johnson is the contact; therefore “Dear Mr Johnston” followed (I would say, being British) by a comma; or (as rodentette would say, being American) followed by a colon.

@chirgy I’m not American. I was taught to write business letters using the British model and I looked up the rules this afternoon when there was the colon/ no-colon debate. The British model doesn’t have any punctuation after the salutation. If you think about it, it would be a bit odd as the the next line of the letter has to contain the subject.

I’m in the UK and I’ve been writing business letters professionally for around 25 years. The British standard is no punctuation at all after the salutation. And none after the “Yours sincerely” either.

In this particular case the OP should put Dear Mr Johnson in the salutation as this is the contact name given. Mr Jonson’s name should also be placed above the receiver’s address too.