This is going to sound a little unkind but as writing skills are such a vital part of marketing and marcomms, I think that we should let the company see your own work without too much of our interference or assistance.
I will say that 'Dear Sir/Madam' is a better salutation, assuming that you do not know the name of the person you are writing to.
'To whom it may concern' (never Dear with this salutation) is only used when you have no idea who will be reading the message - you do know that this will be read by their HR department, or marketing department, or someone connected with the recruitment. It's too vague and could come across as quite rude.