That is a no-no. You should never address a letter unless you know at least the name or the gender of the person. Real life forces us to though, so commonly accepted salutations are:

Dear Sir or Madam:
Dear Madam or Sir:
To Whom It May Concern:


>>Hi Naomi,
>>
>>Miss is an unmarried woman and Ms is for when the marital status is unknown
>>
>>
>
>Thanks, Tracy. How would you start your letter if you're addressing a person with an unknown gender and marital status?
>
>
>>>Hi Andrews,
>>>
>>>Mr. = Mister
>>>Mrs. = Mistress (e.g. married woman)
>>>Ms. = Miss (e.g. unmarried woman, but used in US more often than Mrs. since the woman marrital status may be unknown to the caller).
>>>
>>>But here in UT I think you don't have to be formal. E.g. you can just call everyone by name, e.g.
>>>
>>>Hi John,
>>>
>>>....
>>>
>>>If you want to be formal, you may say "Dear Sir" or "Dear Ms. " + Last Name of the person. But what if you do not know the gender? Would you write Dear Sir/Madam? I use this form in some of my cover letters, but I doubt it's correct...
>>>
>>>
>>>
>>>>Excelent answer Mrs. John; I allready got it....
>>>>
>>>>Thanks for you help...
>>>>
>>>>Keep in toch