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00Greylisting means that the server will initially reject mail from unknown senders and then accepts the message up on the second attempt. This involves a greet delay, so messages will have to wait a few seconds before being accepted. Legitimate mail will wait, but spam will generally not. Further information: https://www.greylisting.org/
Enabling this along with tarpitting can even more effective in reducing spam. For documentation on how to enable tarpitting, click here: http://www.interworx.com/support/faq/enable-tarpitting-reduce-spam/
Set Up:
To enable greylisting, follow these steps:
1. At the command line, use the text editor to view /etc/tcprules.d/tcp.smtp. It will look similar to the following:
127.:allow,RELAYCLIENT="",JGREYLIST="" ::1:allow,RELAYCLIENT="",JGREYLIST="" :allow,LANG="en_US",QMAILQUEUE="/var/qmail/bin/simscan",CHKUSER_MBXQUOTA="99",JGREYLIST_DIR="/var/qmail/jgreylist",JGREYLIST=""
2. On the line that begins with :allow, if JGREYLIST="" exists, delete JGREYLIST=".
3. On the line that begins with :allow, if JGREYLIST_DIR="/var/qmail/jgreylist" does not already exist, add the following: JGREYLIST_DIR="/var/qmail/jgreylist". Example:
127.:allow,RELAYCLIENT="",JGREYLIST="" ::1:allow,RELAYCLIENT="",JGREYLIST="" :allow,LANG="en_US",QMAILQUEUE="/var/qmail/bin/simscan",CHKUSER_MBXQUOTA="99",JGREYLIST_DIR="/var/qmail/jgreylist"
4. Using the text editor, open service/smtp/run.
5. Make sure that the GREYLIST variable is listed and is also not commented out. It should point to /var/qmail/bin/jgreylist Example:
#!/bin/sh QMAILDUID=`id -u vpopmail` NOFILESGID=`id -g vpopmail` MAXSMTPD=`cat /var/qmail/control/concurrencyincoming` BLACKLIST=`cat /var/qmail/control/blacklists` SMTPD="/var/qmail/bin/qmail-smtpd" TCP_CDB="/etc/tcprules.d/tcp.smtp.cdb" RBLSMTPD="/usr/bin/rblsmtpd" HOSTNAME=`hostname` VCHKPW="/home/vpopmail/bin/vchkpw" GREYLIST="/var/qmail/bin/jgreylist" ARCH=`uname -i`
6. Set permissions on /var/qmail/jgreylist so that it is owned by vpopmail:
[root@localhost tcprules.d]# ls -ld /var/qmail/jgreylist drwx------. 2 root root 6 Apr 11 2016 /var/qmail/jgreylist [root@localhost tcprules.d]# chown vpopmail:vchkpw /var/qmail/jgreylist
6. Restart smtp using the following:
service smtp restart
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