1.Uploading the application:
cd /var/www/imscp/gui/public/tools/
//Delete or backup old webmail
mv webmail webmail_old
//Download AfterLogic: http://www.afterlogic.org/download/webmail-lite and upload your web server
wget http://www.afterlogic.com/download/webmail_php.zip
tar xvfz webmail_php.zip
chown vu2000:www-data webmail -R
2.Running web-based installation wizard:
Open http://admin.your_server_name/tools/webmail/install/ page in your browser and follow the instructions
After completing the instructions of the installer, you'll be redirected into AdminPanel:
http://admin.your_server_name/tools/webmail/adminpanel/
Don't forget to delete install directory from the WebMail Lite PHP folder.
3.Test:
http://your_server_name/webmail/index.php
4.Documentation:
http://www.afterlogic.com/wiki/WebMail_Pro_6_PHP_documentation
It's work..