I have an internal apache webserver on our LAN, named castor.foo.bar. The server provides access to documentation areas and user's home directories on castor.foo.bar.

I wanted to make this server available from the internet safely, so I redirected port 80 to port 443 on castor.foo.bar by stunnel, and forwarded port 443 of castor to port 443 of our internet firewall machine mail.foo.bar (we have only this one domainname registered).

I can connect to the webserver using https://mail.foo.bar/, and I can view any documents in and under the server's document root directory, but I have problems with links pointing out of the document root directory of the server: when clicking to such links, I get errors like 'castor.foo.bar not found'.
This is the case e.g. when I try to connect to user's home directories. (https://mail.foo.bar/~username)

I know this error is due to the fact that I connect to the server using URL https://mail.foo.bar/, while the apache server knows itself as castor.foo.bar.

If possible, I want to avoid advertising castor.foo.bar as a registered domain name on the internet, i.e. I would prefer further using URL mail.foo.bar.

Do you know a workaround, maybe an apache configuration option addressing this situation?

Try setting the ServerName directive in httpd.conf to mail.foo.bar then restart apache.

I already tried that, it had no effect.

Meanwhile I found that the problem is more serious: browsing any directories even in the document root gives the same error message (castor.foo.bar not found).

What are your urls in the html referencing? just from the document root or the whole url?

An example:

Entering the following URL from within our LAN shows the contents of directory /usr/local/www/Web/documents in server castor:
http://castor.foo.bar/documents/

Entering the following URL from outside our LAN gives nothing but the error:
https://mail.foo.bar/documents/

Since the document root is /usr/local/www/Web for both virtual servers (castor.meei.hu and mail.meei.hu), both URL should point to the same directory.
From the outside, I can only view html files, and documents to which a relative link points from a html file.
Any html pages auto-generated by apache, like contents of a directory, even if within the document root path, fail to show up if requested from the outside.

Can you post httpd.conf

I am sorry to mislead you (and myself), but the problem turned out to be due to missing trailing slashes when typing in the URLs of directories.
I was misled by the error message: 'unknown machine: castor.foo.bar' which did not help me in the right direction.
Anyway, thanks for you kind attention.

No problem - good to know you got it working .