I am wanting to write a letter to advertise my business and services. I know the person I am writing to, but not personally.
Should I address it
'Dear sir or madam'
'Dear Mr. Bloggs'?
Welcome to Using English, Toolman!
If you know the addressee's name, it's best to use it ("Dear Mr Bloggs").
If you don't, "Dear sir or madam" is fine.
Not a professional ESL teacher.