Sending out a mass email isn’t a good idea for two reasons. First, it’s lazy. If you’d like people to take the time to read your email, do them the courtesy of writing an individual message. For those serious about a career in the music industry, each email should be taken seriously. Do your homework, don’t just go fishing for replies by emailing all the results from a “music industry contacts 2017”: search.
Second, mass emails represent a breach of trust. If you are lucky enough to have a music industry contacts list, they probably don’t want their information shared with others, so don’t cc lots of other people in your emails. It looks unprofessional and careless.