Greylisting

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At the risk of being off-topic I just had to share this.  My apologies to
people who already use grey listing, but if you don't, it appears to be
worth the effort.

I installed a grey listing policy server for postfix (gps) on my mail server
on the 20th.  Here are the spam counts around that date:

2006 Dec 18 Mon .obvious                            980
2006 Dec 18 Mon .spamprobe                           30

2006 Dec 19 Tue .obvious                           1636
2006 Dec 19 Tue .spamprobe                           71

2006 Dec 20 Wed .obvious                           1234
2006 Dec 20 Wed .spamprobe                           54

2006 Dec 21 Thu .obvious                             83
2006 Dec 21 Thu .spamprobe                           19

2006 Dec 22 Fri .obvious                             56
2006 Dec 22 Fri .spamprobe                           14

.obvious is the folder I put spams with very high scores into.  .spamprobe
is the folder I put less obvious spams into.

I installed gps at 5 pm on Wednesday so the total for the 20th only reflects
a partial day with grey listing enabled.

Although 1 day does not a trend make a 90% drop in spams processed by
spamprobe has to be taken seriously!  This was using just a 3 minute timeout
value for the greylist so it is hardly adding any delay at all to incoming
email from unknown addresses.

So, if you run a busy server and want to reduce your load, grey listing is
definitely worthwhile.  It's not a replacement for SP but it clearly has
value in reducing your server load.

All the best,
++Brian



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