If anyone is trying to find potential leads by building relationships with their customers, I can't recommend 'Mailshake' enough! At The Big Phone Store, we use Mailshake. It allows you to personalise each email you send to your customers so that you can include a first name, last name and even a topic that is specific to that customer. It essentially gives you the tools that you need in order to send huge amounts of emails that are all personalised.
The pro's of Mailshake include their lead catcher (A tool where Mailshake will detect which replies are leads and then allow you to assign people to them). You can also 'clean' your contact's email addresses to get rid of any emails that are very likely to bounce back and not be delivered to the intended recipient.
The con's of Mailshake is mainly the amount of emails you can send - but this is not a fault of Mailshake as it uses your own email domain to determine how many emails can be sent on a daily basis (If your email address is fairly new and you don't send many emails, then you will only be able to send around 10 emails per day until you have built your 'reputation').