Not sure about lead sources but for your current list, maybe exporting it into excel and then adding profile properties based on the URL of the email? (Assuming the email they used is their school email.)

If not, could send an email to take them to a page to get more info about them (maybe use Typeform or a modified preferences page). 

@cmfinigan you could make a segment where the email contains .edu

Hey @cmfinigan,

Definitely agree with both @Mailbox Manny and @chelsgrove on the methods they’ve provided on how to segment and locate those .edu email addresses from your own subscribers. 

I would also highly avoid using third-party sources to try to gather emails. That method, which is similar to buying a list or scraping for emails is against our Klaviyo’s Acceptable Use Policy. In addition, because those users have not subscribed to your brand explicitly, this could cause permanent damage to your sending reputation. 

David