There are a few ways of sending out mass emails to customers or potential customers. In my experience, buying lists of “opted in” email addresses very often has poor or no results and can actually end of having a negative effect as people can be annoyed that you have contacted them. Also many companies will not allow you to send emails through their servers if you have not got permission directly from the recipient (gathered the information yourself).
The way to get great results is to only contact people that have requested information or you have direct authority to contact.
When creating the email to send, it may be nice to add their name to it so that they feel it is a little more personal. Make sure that the email you are sending out is going to be of interest, often adding a special offer or discount code works well. It is illegal to send out any marketing emails to anyone without having a “unsubscribe” option within it which will remove them from future emails.
Try not to use words like free and to add too many links to external sites as these are often indicators of spam and may get blocked by many of the recipients email filters.