Have you taken up the double opt-in method?

Sending away random mails to random people is not going to fetch you anything much. However, with an opt in mail you are sure to have connected only with those who have agreed to listen to you.

When you use the double opt-in method, you're targeting only those subscribers who really want to hear from you. But when you are going for the double opted-in lists, they have a much higher engagement levels over time which translates to more opens and clicks and lesser bounce and unsubscribe rate.

In ROI terms, your investment will stay fairly low while your return will increase your spam complaints. This will come down drastically as you people who have opted in cannot include their friend,  co-workers, neighbors etc who didn't give permission to be added to the list.

If a person or malicious bot enters an The mails will not reach those who have accidentally reached on to your website.  No more abc or xyz logins. They have to have a valid email address to opt-in.
You're protected from competitors signing up for your list and then maliciously reporting your emails as spam.

Looking for an opt in mail database?