LOAF
is a simple extension to email that lets you append your entire address book to outgoing mail message without compromising your privacy.

why?

When you receive an email from an address you have not previously written to, LOAF checks to see if the email address is known to any of your existing correspondents. This essentially sorts incoming email into three categories:

Mail from complete strangers
These are people whom you do not know, and who are also unknown to your correspondents.

Mail from partial strangers
These are people you have never sent email to, but who have gotten email from at least one of your own correspondents. This email may deserve more attention, since at least one of your correspondents took the time to write back to the person.

Mail from people you know.
This last category consists of people whom you have written to before. Presumably this is email you’re most interested in, unless it’s another forward from your mom.

This is a bit like Friendster or Linkedin for email