On Tue, 4 Mar 2003, Hadmut Danisch wrote:
I don't know of any text filtering that works reliably and reasonable.
SpamAssassin is excellent. But you are right, there can be false-positives.
And, I believe that is is a bad idea to perfom text analyse _while_
receiving the message. Message transfer should be as fast as possible
and should not suffer from any external delay.
If you limit the size of messages you scan, and implement things
intelligently, SpamAssassin can scan messages in 100 - 500
milliseconds on cheap PC hardware. This includes MIME decoding and
attachment-unpacking, etc.
The typical mail server is not CPU-bound, so adding content-scanning often
just improves the resource balance. :-)
And it is not always
possible because some formats can be decoded/uncompressed only when
they are complete.
The scanning is done at the end of the DATA phase while the sender is
waiting for the final acknowledgement. The recommended timeout here
according to RFC 2821 is 10 minutes, so adding under a second of
content-scanning shouldn't be a problem. The only drawback is what I
alluded to in a previous post: SMTP doesn't allow success for some
recipients and failure for others at the end of the DATA phase.
I don't like text analysis while receiving the message. And I am
not really convinced about such content methods.
Try them out; I think you'll be pleasantly surprised.
--
David.
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