Centos 7 squirrelmail Forbidden You don't have permission to access /webmail on this server.

I followed online articles to install postfix,dovecot and squirrelmail on Centos 7, but got error when accessing http://serverip/webmail:
Forbidden You don't have permission to access /webmail on this server.
in httpd error log: /var/log/httpd/error_log:
AH01630: client denied by server configuration: /usr/share/squirrelmail
after lots of Google search, this is due to httpd 2.4 access control has changed from previous version:
in /etc/httpd/conf/httpd.conf
Order allow,deny
Allow from all
should be replaced by:
Require all granted
then restart httpd:
#systemctl restart httpd
problem solved!
refer to: http://httpd.apache.org/docs/2.4/upgrading.html#access
Very useful tools to find out configuration errors of your email server:
postconf -n
doveconf -n