How can I effectively use this email address list to engage prospects? Can social media help?

I have a list of over 10,000 email addresses collected organically from the website. They were collected over the past several years using single opt-in. The open rate on emails to this list is currently less than 10%. I have now switched to a different email app (email service provider) and am now using a double opt-in system to collect leads on the website. I am reluctant to add bad email addresses into the new email app. What options do I have for using this email address list to engage or communicate with prospects? Is there a way to use social media to connect with prospects from this list? For most records, I have first name, email address, and IP address; for a smaller subset I have additional information like city, state, zip code etc…