1)
-Change into you Plesk Admin htdocs directory (e.g. /opt/psa/admin/htdocs)
-Make a directory for the Greylisting Manager (e.g. "mkdir glm")
-Set chown of the directory you made above to root:psaadm ("chown root:psaadm glm")
-Set chmod of the directory you made above to 755 ("chmod 755 glm")
-Extract all files of the ZIP into that directory
-Set chown of all files to root:psaadm ("chown -R root:psaadm *")
-Set chmod of all files to 755 ("chmod 755 -R *")
-Set the wrapper to chown root:root ("chown root:root wrapper")
-Set the wrapper to chmod 4755 ("chmod 4755 wrapper")

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IMPORTANT THE GLM DON'T WORK ON PLESK LOWER THAN VERSION 9!!!
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-make your settings in file config.inc.php

2)
-Login to your Plesk as admin
-Make a new Custom Button with the following settings:

Button label: Just choose a name ;-)
Location: Domain administration page
Priority: 100
Background image: choose the glmlogo.gif of the ZIP
URL: your directory you made above an the index file (e.g. "/glm/index.php")
Include domain id: yes
Include domain name: yes
Include FTP Login: no
Include FTP password: no
Include client id: yes
Include client's company name: no
Include client's contact name: no
Include client's e-mail: no
Context help tip contents: whatever you want
Open URL in the Control Panel: yes
Visible to all sub-logins: yes (if your clients are allowed to use the glm)