Following on from my previous post about greylisting read the full version of this entry to see some stats before and after deploying it on my secondary MX.
Greylisting only on the primary MX:
Average mails tagged as spam per day before (10 day average): 153
Spam tagged for the day with just primary doing greylisting: 93
Greylisting on secondary MX only:
Average mails tagged as spam per day before (10 day average): 153
Spam tagged for the day with just primary doing greylisting: 40
Mail stats for secondary server:
2004-10-17:
TOTAL Volume Messages Hosts
Received 4980KB 1135 333
Delivered 4973KB 1165 13
2004-10-18:
TOTAL Volume Messages Hosts
Received 12MB 1583 463
Delivered 12MB 1646 9
2004-10-19:
TOTAL Volume Messages Hosts
Received 44MB 1602 446
Delivered 45MB 1641 14
2004-10-20:
TOTAL Volume Messages Hosts
Received 4509KB 78 18
Delivered 4679KB 76 5
That is a HUGE reduction in spam mails entering the systems. I am very happy with this. Looking through the list of machines that I received mail from in the days before greylisting they are mostly dynamic hosts and other weird places. Looking through the list of the last day they are all legit machines and only one of them can immediately be related to bulk mail sending.
If I look at the remote hosts my machine communicated with, I can see that the advantage passed onto the people I am secondary for is huge, for my own primary MX the amount of mail dropped from 208 on the 19th to 7 on the 20th.
A hidden benefit from all this is that maintaining my secondary server has become much easier, previously it would always have large amount of bounces that was failing to deliver and eventually got frozen as well as large amounts of mail sitting there being rejected by MTA's doing SMTP time spam checking. Now, that's all gone!
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