How to: Enable Greylisting to Prevent Spam

Greylisting means that the server will initially reject mail from unknown senders and then accept the message upon 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 can be found here.

Enabling both greylisting and tarpitting can be even more effective in reducing spam. Documentation on how to enable tarpitting can be found here.

Contents

• How to: Enable Greylisting to Prevent Spam

  • To Enable Greylisting

To Enable Greylisting

1. Log in to the server at the CLI as root, either via SSH or from the terminal

2. At the CLI, use the text editor to open /etc/tcprules.d/tcp.smtp. By default, the contents of the file should look similar to the following:

   127.:allow,RELAYCLIENT=""
   ::1:allow,RELAYCLIENT=""
   :allow,LANG="en_US",QMAILQUEUE="/var/qmail/bin/simscan",CHKUSER_MBXQUOTA="99"
   

3. Add ,JGREYLIST="" to the end of the first two lines. The /etc/tcprules.d/tcp.smtp file on some servers will have this information included by default. If that is the case, this step can be skipped

   127.:allow,RELAYCLIENT="",JGREYLIST=""
   ::1:allow,RELAYCLIENT="",JGREYLIST=""
   :allow,LANG="en_US",QMAILQUEUE="/var/qmail/bin/simscan",CHKUSER_MBXQUOTA="99"
   

4. On the line that begins with :allow, add JGREYLIST_DIR="/var/qmail/jgreylist"

   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"
   

5. Save and exit the text editor

6. At the CLI, use the text editor to open /service/smtp/run. By default, the beginning of the file should look similar to the following:

   #!/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`
   

7. Uncomment the GREYLIST variable by removing the #

   #!/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`
   

8. Save and exit the text editor

9. At the CLI, make sure that the /var/qmail/jgreylist directory is owned by so that it is owned by vpopmail:vchkpw

   [root@server ~]# ls -ld /var/qmail/jgreylist
   drwx------. 2 vpopmail vchkpw 6 May 12  2020 /var/qmail/jgreylist
   [root@server ~]#
   

   • If the directory is not owned by vpopmail:vchkpw, update the permissions

     chown vpopmail:vchkpw /var/qmail/jgreylist
     

10. Restart smtp

    service smtp restart