Castle - The easiest way to protect your users from getting hacked
Antideo - Email, IP address and phone number validation API service
Mail Dump - Powerful Extensions for email addresses extracting, verifying and finding
Verifier - Weed out disposable, non-existent domains or invalid emails.
Truecaller - Find a person by a name or phone number worldwide for free using Truecaller.
Proofy - Quickly validate and verify your email lists.