403 Forbidden. You don't have permission to access /webmail/installer on this se

[wp.rauchholz]

I run postfix/dovecot apache 2.4 server, php71 under CENTOS. With Thunderbird I can send/receive emails. I use port 993 for IMAP
I installed roundcubemail. I cannot get passed the login screen. I get the following error message

[16-Mar-2018 10:14:34 +0100]: <j76pt0vd> IMAP Error: Login failed for wp.rauchholz@<mydomain> from 165.225.76.124(X-Forwarded-For: 83.58.81.163). Could not connect to <mydomain>:993: Connection timed out in /var/www/<mydomain>/html/roundcubemail/program/lib/Roundcube/rcube_imap.php on line 196 (POST /webmail/?_task=login&_action=login)


Port 993 in firewall is open
-A INPUT -i ppp0 -p tcp -m state --state NEW -m tcp --dport 993 -j ACCEPT

I changed .htaccess file to: <IfModule mod_php7.c>

I created a roundcube.conf file that looks like this:
Alias /webmail /var/www/<mydomain>/html/roundcubemail

# Define who can access the Webmail
<Directory /var/www/<mydomain>/html/roundcubemail/>
<IfModule mod_authz_core.c>
    Require host <mydomain> (I also tried require up <server IP>
    Require all granted
    DirectoryIndex index.php
</IfModule>
</Directory>

# Secure access to installer
<Directory //var/www/<mydomain>/html/roundcubemail/installer/>
<IfModule mod_authz_core.c>
    Require ip 10.5.2.1
</IfModule>
</Directory>

# Directories that should not be viewed by Web clients.
<Directory /var/www/<mydomain>/html/roundcubemail/bin/>
    Order Allow,Deny
    Deny from all
</Directory>
<Directory /var/www/<mydomain>/html/roundcubemail/plugins/enigma/home/>
    Order Allow,Deny
    Deny from all
</Directory>

I tried to re-run installer and get now a 403 Forbidden.

Wham am I missing?

Thank you, Wolfgang

[SKaero]

So that error has nothing to go with any of your apache configuration. I'd suggest trying to change the imap host to localhost instead of your domain and see if that allows you to connect.