I've been monetizing fresh / targeted third-party email for almost 17 years.
Unless you are familiar with third-party data, it is email data where users have shown interest in a particular niche and have given permission to receive third-party messages. You get the opt-in record for all users and it's 100% spam compliant.
I mainly receive data that appeals to users' interest in various PPL offerings (pay per lead … lead generation). This is because no credit card / purchase is required to complete an offer. A user just has to fill out a form, so conversion rates tend to be much higher when compared to offers that require a sale.
The bottom line is that it's much easier to get someone to fill out a short form than to take his credit card and make a purchase. So why not try to sell this or that if you can provide information that users actually want / need, and get paid for it well.
Some of the sectors (niches) with which I have had very good experiences are: insurance, education, debts, credits, loans, mortgages, assistance, discounts, offers for homeowners, etc.
Basically, I'm monetizing the data with PPL offerings because they offer the path of least resistance to generating conversions ($$$) and converting the data into money-producing assets.
There is a lot more to it, but done right it can be extremely profitable. Anyone I know he's in business and knows what he's doing makes up mostly 6-7 numbers. While this may be an enormous range, much depends on whether you can scale and effectively manage the infrastructure that needs to be scaled.
Something to think about.