End users have it easy with spam. They only have to delete a few hundred messages a day. For real spam misery, try being a network or e-mail administrator, with tens of thousands of daily spam messages clogging up your network pipes or mail server's storage.

Fortunately, an old approach, mail server authentication, which has often been suggested to stop spam, may be making a return in a variety of new forms. The tack is to modify how Simple Mail Transport Protocol (SMTP) works.

Today, when a mail server gets a message from any SMTP client, it passes it on to its destination without bothering to check if the user or domain is legitimate. It's that very trick that worms like MyDoom, Gibe, and Netsky use to turn infected systems into spam-generating machines.


SMTP's other problem, as anyone who has ever received spam from what appeared to be a friend knows, is that it doesn't do a decent job of stopping spammers from spoofing (aka forging) e-mail headers. Besides making you open messages you otherwise would never have touched, it's this security hole that makes phishing messages (e-mails that appear to be from companies you deal asking for personal information) the bane of naïve users today.

So what can you do about it? Well, some have suggested that SMTP, which was written in an era when all computers were trusted, simply be dumped and replaced. While this is an interesting notion, it hardly seems likely to happen, given that SMTP has displaced all other would-be popular Internet-level mail protocols such as X.400. For better or worse, it's an SMTP world.

There have also been attempts to modify SMTP. For example, there is already an Internet Engineering Task Force (IETF) SMTP over SSL/TLS protocol Request for Comment (RFC) - 2821. However, using this (or other such methods) requires that servers, if not users, be authenticated as being legit by some third-party directory service.

Other approaches, such as RFC-2015, would use MIME Security with Pretty Good Privacy (PGP) for authentication. Until recently, these ideas got more lip service than practice, but now major companies like Microsoft, Sendmail, and Yahoo are moving in the authentication direction.

Sendmail, which claims that its self-named e-mail server is used by seven of the Fortune Top Ten companies, will work on developing and distributing sender authentication technologies. This doesn't mean, however, that Sendmail will be creating its own authentication scheme. Instead, Sendmail appears to be looking towards Yahoo's DomainKeys and Microsoft's "Caller ID for E-Mail."

DomainKeys would incorporate a public-key authentication system on top of SMTP. This would work by having each message be digitally "signed" with a digital signature and public key for each domain. On the other side, the receiving e-mail system uses the public key to validate the signature. Since this signature is incorporated as a new header, and SMTP can already handle such headers, mail administrators would not have to update their mail servers.

They would, however, have to use a preprocessing program or an add-on to their existing mail server in order to authenticate these signatures. In addition, as with any public key encryption system, this system would require a trusted third-party directory system to ensure that the keys are authenticated.

All this puts more of a load on the mail server. On the other hand, the overall load on the mail server and network should be reduced since it will no longer be at the mercy of having to send on much bulkier spam messages. Another plus for this method is that it requires absolutely nothing from end users.

Page 2: Microsoft's Caller ID for E-Mail