http://www.yesware.com/blog/find-email-addresses/

How to Find ANY Email Address Contact in 2 Minutes

https://www.quora.com/If-I-have-someones-email-address-how-can-I-find-out-about-their-social-media-accounts

https://www.searchbug.com/peoplefinder/results.aspx?TYPE=people&WHAT=Email

http://www.emailsherlock.com/

7 Best Rapportive Alternatives

https://martin.kleppmann.com/2013/10/23/linkedin-intro-doing-the-impossible-on-ios.html

Spokeo

Pipl

FullContacts

LeadIQ

RocketBolt

Intelius and Zaba

https://clearbit.com/

https://msdn.microsoft.com/en-us/office/office365/api/people-rest-operations

https://pipl.com/dev/

https://maildb.io/queue#features

https://www.toofr.com/get

https://anymailfinder.com/

https://everifier.org/

freshaddress : used at websphere

BULK EMAILs

https://kvnmail.com/email-extractor.html

duocircle

mailchannels