The BPO writers can write to these users because they have already shown an interest in the brand or the client that you are working to promote/market. You will be able to cut more ice with them than totally disinterested consumers. Email lists are not going to work for you that way. It's better if you create an email list of your own by sourcing email ids from traffic visits. Encourage your users to write emails to you or subscribe to your newsletter. Newsletters are a great way to reach out and connect with your external and internal publics email list. Answering emails written by the users can easily quality as great customer service. Email lists are often misleading in terms of data. It may take the lead generation process to a completely different trajectory. For example, you may end up making telemarketing calls to people who don't exist! Email lists often contain defunct email ids, ids of people who are now dead or simply not using that id anymore. These databases are hardly cleaned and are packed with spam traps, bots and other ways that email service providers use to prevent spamming. BPO units have to ensure that they are using a clean database whenever they think of sending emails.