There is a successful pattern of marketing using email broadcasts.
There are also many wrong or bad ways to go about it. It's best to stick to this pattern closely:
1. Accumulate an email list of customers, prospects, anyone interested. Or, rent a list, but only "managed lists" such as from a magazine or association. They will send out your broadcast for you, and it will not be cheap (possibly 35 cents an address). There are no other legitimate ways to get email lists.
You are only interested in individuals who have expressed an interest in you or who are highly likely to be interested in what your are offering
2. If you have the opportunity to specify the subject line, think through carefully how to word it. Be truthful, but say something that will interest genuine prospects.
3. Make your broadcasts mostly text. If it is all in a picture, most people will never see your ad as they will not open your email on speculation. Make sure that what is "above the fold" (what they will probably see without scrolling down) is interesting enough to make them want to read on.
4. Make your communications mostly material of general interest to the people you are communicating to. Your commercial messages should only be a small percentage of what you send out. So if you have a newsletter make it 80% news and 20% ads. After all, most people don't subscribe to newspapers and magazines for the ads. Why should they subscribe to your email broadcasts for the ads? (in some cases of course, they will.)
5. Handle any unsubscribe requests, bad email addresses and complaints promptly.
Email broadcasting can be hugely successful. Successful email campaigns usually follow these rules.