If you want to run a mass mail out to companies to promote a product or service you are offering then you will need to spend a bit of time researching email addresses to make sure you get the best response to your mail out. You can often buy lists of email addresses but this is illegal unless you have permission to email them and also many mail out companies will not allow you to upload such lists and send out using their servers.

If you are going to be using your own servers o send the mail out from, then firstly check with your hosting company as to how many emails you can send out at one time and also check that the data you have is genuine and does not contain spam email address that may end up blacklisting your server IP address.

The best way to get good data to email to is to call up companies and ask who you should email details through to. Also try and get a contact name so you can personalise the emails to an individual rather than just sending a generic one as this have proven to get better results in terms of open rates etc.