Spam - 14: Sendmail 8.9 - The Spam Control Release
Dateline 03/23/98
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"Baby, I checked it out. I think you ought to know.
Van Halen |
Why an anti-spam release?
Spam is a nuisance, spam is a problem, spam costs a lot of money. Spam is bad.
Why sendmail?
Spam is no technological problem and thus a 'real' solution will not be a technical one. Yet, technology can help. This can most effectively done at the mail server level and this is why strong anti-spam features in sendmail are important.
There are other "Mail Transport Agents", notably qmail, that incorporate features which limit spam. The spam control version of sendmail is far from being something new or revolutionary.
Still, reportedly controlling 76% of the mail server 'market' (sendmail is free) on UNIX, it may be revolutionary concerning the impact. In the past, hosts have been reluctant to convert to the spam-disabling server software, notably again qmail, which represents a quite different mail handling and program maintenance approach.
Of course not everybody will convert to the new version at once (sendmail 8.9.0 is currently available as beta 3 for download) but it has become easier than ever to actively implement an anti-spam policy at the SMTP server level.
What's in it?
The probably most important change in version 8.9 is that relaying is turned off by default. This means that only mail coming from a predefined list of hosts will be relayed to non-local users.
With the new release it is possible to limit the size of the argument to the EHLO/HELO command. This is where spammers try to hide their whereabouts in long "Received:" lines.
Sendmail now supports regular expression matching on email addresses and thus allows filtering of really suspicious ones.
Related to the last item, sendmail allows sorting out messages based on the contents of header fields. This makes it possible to implement something similar to our spam filters at the server.
The new release made it much easier to use the MAPS Realtime Blackhole List. This is a list of known sources of spam that are blocked entirely.
The default settings disallow mail with an invalid host name in the return address. This is a somewhat double-sized sword as spammers can easily adapt to that, but if they do this has mostly negative results: bounces and complaints will go to a legitimate user.
A new option makes it possible to limit the number of recipients per message. Traditionally, this has worked well, but with new bulk email software turning to sending mail directly to the recipient it should be less important. The new spamming strategy makes it easier to trace back spam, so it is hardly a improvement for spammers.
A new mailer, "discard" accepts a message only to throw it away.
