In "Another Whack at Spam", Tim Bray describes a solution similar to my Trusted E-mail Network (TEN) idea (also read "Fixing E-Mail") – via Dave whose blog I read before Tim's blog.  He arrived at the solution while talking about spam at Foo Camp with Jeremy Zawodny, Dave Sifry, and Doug Cutting.

He also thinks digital signing should be done by mail servers instead of users.  But his thinking differs from mine in how the trusted network of mail servers should be organized and the network's relationship with mail servers outside the network.  I believe the network should be backed by a business entity in charge of issuing and revoking certs to member mail servers, maintaining and providing trust rating information on mail servers and mail users, etc.

While I like loosely-coupled peer network as much as anyone, I believe PKI and responsiveness requirements call for a central authority.  Under Tim's solution, each mail servers are given too much room for misbehavior and removal of a rogue mail server takes too much time.  What I want is the ability to shutdown a rogue user or mail server within hours, not days.

Update #1 – 10/13/2003 11:15AM PST

Liz Lawley raised some key concerns that reminded me to fill in some missing pieces of the TEN model.

Open Source

Since there is nothing proprietary about TEN servers, there will be plenty of open source TEN-enabled mail servers and TEN-enabling patches for popular open source mail servers.  So TEN servers will be very affordable.

Private E-Mail Network

TEN servers should be able to use multiple PKI.  This means each TEN server will have multiple certs to sign e-mails with depending on the source and the destination of each e-mail.

If the mail exchange is completely within an organization, the message can be signed with a self-signed cert after checking to see if the sender meets the private TEN's trust rating requirement.  For mail sent outside the private TEN, a public TEN cert assigned to that TEN server should be used but only if the mail sender has sufficiently high TEN rating.

Free or Subsidized

A Private TEN does not have to charge fees.  For example, American universities can form a national private TEN, with each university or department running their own TEN server, that allows students and staffs from any of the member universities to exchange e-mail with each other without a fee.  Some universities could even sponsor some percentage of the fee for e-mails sent outside the University TEN.

Global Trusted E-Mail Network

While anyone can run a TEN server, not everyone will be able to get a Global TEN cert that enables e-mails to be trusted by anyone world-wide.  There are three ways to get a Global TEN cert:

1. Implicit Trust – you are trusted without doubt or reserve
2. Bonded Trust – you put up money to be trusted
3. Sponsored Trust – you are trusted by someone with a Global TEN cert.

Implicit and bonded trusts are obvious so I won't go into details about them unless someone asks.  Sponsored trust means a there is relationship between the sponsoring organization and the sponsored.  Each trusted mail sent from a sponsored organization affects both organizations if a complain is lodged against the mail.

For example, if a Stanford physics student sends out a mail with virus to someone, trust rating of Stanford Physics Department's TEN server and Stanford's TEN server will be degraded because the school sponsored the department.  If Stanford is a member of American University TEN, then the American University TEN's trust rating is degraded.