============================================

apt-get install courier-pop

apt-get install courier-pop-ssl
 /etc/courier/pop3d.pem or /etc/courier/imapd.pem.
 
configuration files in /etc/courier

/usr/sbin/authtest
/usr/sbin/courierlogger
/usr/sbin/authpasswd
/usr/sbin/authenumerate

============================================

squirrelmail

/usr/sbin/squirrelmail-configure

$ ln -s /etc/squirrelmail/apache.conf /etc/apache2/conf.d/squirrelmail.conf

# File /etc/apache2/sites-available/webmail
<VirtualHost *:80>
  ServerAdmin [email protected]

  DocumentRoot /usr/share/squirrelmail
  ServerName webmail.datahunter.org

###################### log #####################
        ErrorLog /var/log/apache2/webmail.datahunter.org/error.log
        LogLevel warn
        CustomLog /var/log/apache2/webmail.datahunter.org/access.log combined
################################################

        ServerSignature Off

</VirtualHost>