Sumo - Free tools to grow your email list.
NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.
OptinMonster - OptinMonster helps to convert abandoning website visitors into subscribers and customers.
Email List Verify - The Fastest Way to Improve Email List Deliverability and ROI
OptiMonk - OptiMonk is the most powerful Onsite Retargeting platform, that helps you increase the conversion rate of your site, and get more leads by recovering lost visitors.
ZeroBounce - Removes invalid emails from your list to prevent email bounces from ruining your deliverability.