Newbie - per 'user' question

Vernon Schryver vjs@calcite.rhyolite.com
Wed Apr 30 20:56:20 UTC 2003


> From: "Edward D. Bryson" <edb@esper.com>

> ...
> With a pair of meshed dcc servers talking to several other dccd's I thought
> the volume on 'my' server wouldn't apply. If my people are 'unlucky' enough
> to get the first wave of a spam campaign a few of them will get it and help
> others not to, if 'your' server got spammed first, i thought the flooding
> interaction would then protect my people even if only one of them got it.

If I understand that, then I agree.  Mailboxes protected by the DCC
can be unlucky.  There are two mitigating effects.  One is that major
spews of spam involve millions of targets, so that being unlucky enough
to be among the first dozen targets is pretty unlucky. 

The other is that bulk mail tends to be send to sorted copies of their
target lists.  Perhaps that is an artifact of spammers removing
duplicates, or perhaps it comes from other mechanisms.  I usually
receive my copies messages from legitimate mailing lists long after
people with addresses near the start of the alphabet.  This means that
if an address that is unlucky once is likely to be unlucky a lot.
Such addresses make dandy spam traps.   For example, my web pages
contain several hidden mail addresses starting with the letter 'a'.
Those addresses are often hit long before "vjs".


> also, just a thought, why not store thresholds as a specially formatted
> 'first' line in the per user whitelist file.

The ASCII whitelist files are used only to generate the binary .dccw
hash tables.  When a message arrives, at most the modification time
of the ASCII whitelist files is routinely consulted.  Only the .dccw
files are routinely checked, and there are mechanisms to minimize the
costs of that including caching file descriptors and memory mappings.
It would be possible to kludge a special checksum hash table key and
value into the .dccw files, but the thought is distasteful.  It would
also be possible to change the format of the header including magic
number in whitelist hash tables.


Vernon Schryver    vjs@rhyolite.com



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