From a UK English point of view .....
On the contrary, if you're writing a formal business letter, it would be quite proper and correct to begin with "Dear ..."
When you don't know the person's name, or if you are writing an initial letter to an organisation, or to someone you don't know even by name, then use "Dear Sir", or "Dear Sirs".
If you have a name for the person, and it is male, such as Ivan Elovanitch, the you would write "Dear Mr Elovanitch"
In UK English, it can be slightly more tricky when addressing a female, because you don't always know if they're single (Miss) or married (Mrs). For example, you might just know a name, like Norah Bone. To get around this, you can use "Dear Ms Bone".
Don't use "Dear Ivan" or "Dear Norah" unless they have indicated in some way that it is acceptable for you to do so, as it is too informal otherwise.
Of course it always pays to do your research first - find out as much as possible about the organisation before you approach them in the first place!