If you want to cover this topic in detail, it requires thousands of words; I don’t, and won’t bother. Email is too deep a system, with twists and turns not only from a technical perspective but also etiquette.
Let’s put spam aside with this one note: Email should never be used to contact a person about what you are doing without the recipient requesting it. It may be used for initial contact, though, if the message is one sentence asking for permission to contact in the future and plainly states, “Unless your response is ‘yes’ I won’t contact you again.”
Putting out an email blast to names that you’ve gathered from a variety of sources is SPAM. You don’t like getting unsolicited emails anymore than the person who gets one about your music or gig dates.