[m.a.g.]

The communication to the proxy is https. As well as the communication between the proxy and Zimbra.

I use the same certifiaces for apache and Zimbra.

my httpd.conf looks like:

<VirtualHost *:443>                                                                                                            
        ServerAdmin webmaster@domain.ch                                                                                    
        ServerName secure.domain.ch                                                                                        
                                                                                                                               
        DocumentRoot /var/www/  

    SSLProxyEngine On                                                                                                          
                                                                                                                                                                                               
    SSLProxyCACertificateFile /etc/ssl/certs/UTNAddTrustServerCA.crt                                                           
    RequestHeader set Front-End-Https On                                                                                       
    ProxyPreserveHost On                                                                                                       
                                                                                                                               
    ProxyRequests Off                                                                                                          
    ProxyVia full                                                                                                              
    <Proxy *>                                                                                                                  
        Order deny,allow                                                                                                       
        Allow from all                                                                                                         
    </Proxy>     
                                                                                                              
                                                                                                                               
    <Location "/zimbra">                                                                                                       
    SetEnv force-proxy-request-1.0 1                                                                                           
    SetEnv proxy-nokeepalive 1                                                                                                 
    ProxyPass https://mail.domain.ch:443/zimbra                                                                            
    ProxyPassReverse https://mail.domain.ch:443/zimbra                                                                     
    </Location>

        SSLEngine On                                                                                                               
    SSLCertificateFile /etc/ssl/certs/secure.crt                                                                               
    SSLCertificateKeyFile /etc/ssl/certs/secure.key                                                                             
    SSLCertificateChainFile /etc/ssl/certs/secure.ca-bundle                                                               
    SSLProtocol all                                                                                                            
    SSLCipherSuite ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+EXP:+eNULL                                                             
                                                                                                                               
</VirtualHost>

Beside this, I have many other 'Location' where I use a proxy for other services on different servers. They all work without any problem. They all use https as well.

So far, I tried all kind of combinations in the config-file...