Before you start sending CDs out, emailing everybody on staff at a company, or calling the headquarters nonstop, try looking at the websites of all of the record labels you’re considering sending music to. Some of them have specifically spelled out policies regarding sending in demos, and these can either be a hindrance or very helpful.
For example, Sony Music has a page on their site saying the company “and its employees do not accept, or consider, unsolicited sound recordings, musical compositions or any other creative materials.” The statement goes on to add, “For one of Sony Music’s labels or creative centers to review a demo, it must come recommended through an established music industry professional, such as a Manager, Lawyer, Agent, Producer, artist, programmer, or tastemaker.”
That might not be what you were hoping to see, but at least you know. Plenty of smaller companies will also have their acceptance policies written down, and quite a few indie labels (especially those further down the totem pole of popularity) will actually provide you with either an email address or a physical address where you can send things. Of course, this doesn’t necessarily mean you’ll hear back, or that somebody will listen, but if it’s how the company wants to be pitched new music, you should at least start there.