I'm looking for library/API to retrieve contact list (emails address to which user had sent mail to, regardless whether user had explicitly added it as contact). Does anybody know such library/API available there?
Please have a look at socialauth. This Java library will help you get the contacts from most of the networks.
Look at: http://openinviter.com/index.php
If you are using php - you might wish to try out http://openinviter.com - its free and supports almost all major social networking sites and mail sites.
I don't think that data would ever be held outside the email headers. What you want is some way to find all the unique addresses in the recipent field of all sent mail items.
For example in Google mail - you could use this project, the Gmail Agent API, to retrieve all the sent item headers. You would then just need to extract the relevant data from them.
I'm sure this technique is possible is for some of the other providers you mention. The Yahoo Api for example looks to provide everything you need to do this.
Look at Octazen: http://octazen.com/. Their software handles all kinds of webmail systems and social networks.
To get (some) details out of Facebook, I've just found (and used!) the Greasemonkey-script/webservice from http://brad.livejournal.com/2398409.html to pull at least the names and some details from Facebook to Google contacts, from where it can be gotten at by other means, such as the Gmail contacts API
来源：https://stackoverflow.com/questions/637560/export-contact-list-from-gmail-hotmail-yahoo-linkedin-facebook