Unless you’re writing to a head of state you really don’t need to be incredibly formal with your writing.
Polite is good.
Do Check Spelling of Names and Correct Titles
People are sensitive about their names. It is a mark of respect to make the effort to spell it correctly whether it’s a letter, email or handwritten note. It may not win you any points, but getting it wrong will surely lose you some.
How to Address People
If you don’t know their name, ‘Dear Sir or Madam’ is an appropriate salutation. If you do know their name but haven’t met them or don’t know them well, use ‘Dear Ms Xx’ or ‘Dear Mr Yy’. If you are already on first name terms with them, if you don’t use their first name they may wonder why you are being so formal, and they may be offended.
How to Sign Off
When you use their name it is usual to sign of ‘Yours sincerely’. If you don’t know their name use ‘Yours faithfully’.
I once received a letter with the sign off, ‘I remain, Sir, your obedient servant’. Clearly this person had forgotten that I was a woman (it was addressed to Ms Dalice Trost) and was following a formula. This formula was frequently used by the armed forces. It really has no place in business life. It is excessively formal, and virtually meaningless.
Business emails are usually less formal than letters. That said, many of the complaints about correspondence from companies relate to excessive informality. If you are emailing someone who has emailed you and you are not sure about which tone to use, mirror the tone that they used. In other words, reply where possible in a similar way to the way that they addressed you. If they wrote ‘hello’, write ‘hello’ rather than ‘hi’.