Around the same time, Microsoft too was much exercised by the challenge of spam. One of the counter-measures outlined by Bill Gates in a speech dealing with the subject was originally dubbed Caller ID for Email. Since this worked in a very similar way to SPF, both parties were under pressure from the industry to combine their efforts. The result was Sender ID: there is an executive background document, deployment overview and an “apology for Sender ID”.

Sender ID has been submitted to the IETF as a draft. An IETF working group known as MARID (MTA Authorization Records in DNS) has a page with some related work, including a paper describing an extension to the the basic Simple Mail Transport Protocol (SMTP) service, one of whose authors is the creator of the popular Sendmail software, Eric Allman.

Sender ID is certainly not a panacea. For example, it could be circumvented by a spammer who registered servers using the free SPF Wizard. More problematic still, zombie networks could be built up from computers with valid Sender ID records. One suggestion is that the mass mailings from such zombie machines could be prevented if it were mandatory to equip high-speed Internet access devices with firewalls.

Technical issues aside, there is another problem with Sender ID. Although Microsoft is offering to licence its Caller ID approach under liberal terms, for some, they are not liberal enough. Richard Stallman, the obdurate conscience of the computing world, has pointed out that adopting Sender ID as an anti-spam standard implicitly aids Microsoft in its increasingly strenuous tussle with free software. In his view, backing Sender ID would mean losing rather more than the annoyance of a few spam messages.

Glyn Moody welcomes your comments.