This is the cardinal sin in contacting record labels! You wouldn’t believe how many people blindly send their demos out with little regard to whether the label they’re contacting is a death metal label, Christian label or even a record label at all. (Yes, this happens. People send their music to businesses with absolutely nothing to do with the record industry.)
Do some research on the artists you love, with a similar sound to you, and find out who has released their records over the course of their careers. If an artist you like is on a major label, look up their discography online and see where they started out. Imagine this scenario: your music has a similar vibe to a hypothetical rapper with a lot of underground buzz, who just signed to Def Jam or a big indie like Rhymesayers.
Who put out this rapper’s early stuff? Is there a hole in their artist roster where this artist used to be — a hole you could fill? Sure, submit your demo to the bigger name labels, but investigate the smaller ones, too. Obviously those ultra indie labels are already on the big labels’ radar, or they wouldn’t be scouting their artists. Plus a smaller label might be the better fit for your music, your artistic world view, and your fanbase.
Another key part of doing your research is finding out the names of the people at the label you’re targeting. Who’s the A&R Coordinator at the label? You can find contact info for pretty much every label you can think of via the A&R Registry.
This will save you a lot of online search time, although you can also try to find this info on the label website, by sleuthing around LinkedIn or Twitter, or by doing a bit of Googling. Addressing these people by name will show you really care about the label and what they have to offer, and you’ve taken the time to get to know them — isn’t this what you’d want from your potential label, too? On an even more basic level, addressing your email or physical mail submission to an actual person at the label gives you a higher chance of them at least opening it.
If it looks like you’re just doing an impersonal mass mailing to fifty randomly-selected labels, people are going to be much less likely to read your email or put your CD on.
A couple more tips: if it says “no unsolicited recordings” on their website, they mean it. Find another way in. Do you have any form of personal or business connection to anyone at the label? Can you make a connection? Creating a spreadsheet can help in properly targeting your submissions, and in keeping track of who you contacted, when, and if they replied or not.