Seems that you are redirecting to yourself:

You need a (virtual)host for servername, in this you redirect to 
servername.mydomain

The (virtual)host servername.mydomain then has the correct SSL 
certificate and so on but does not redirect to somewhere else.

> Does not work. I get an error message "Redirection limit for this URL
> exceeded. ...".
> 
> By the way: the reason I have to do is is the certificate which was
> created for "servername.mydomain". So everybody who just types
> "servername" has to accept the certificate. I want to avoid this.
> 
> Pedro
> 
> ----------------------------------------------------------------
>   
> 
> >Hello
> >
> >Within a virtual server I want every request of the form 
> >https://servername <https://servername/> to be redirected to 
> >https://servername.mydomain <https://servername.mydomain/> . Can 
> >somebody give me a hint which RewriteRule and RewriteCond I have to
> >    
> >
> use?
>   
> 
> >Thanks' in advance for any help
> >
> >Pedro
> >
> >    
> >
> 
> In (virtual)host for https://servername
> 
> RedirectMatch / https://servername.mydomain/$1
> 
> 
> ---------------------------------------------------------------------
> The official User-To-User support forum of the Apache HTTP Server Project.
> See <URL:http://httpd.apache.org/userslist.html> for more info.
> To unsubscribe, e-mail: users-unsubscribe@[...].org
>    "   from the digest: users-digest-unsubscribe@[...].org
> For additional commands, e-mail: users-help@[...].org
> 
>   
> 

---------------------------------------------------------------------
The official User-To-User support forum of the Apache HTTP Server Project.
See <URL:http://httpd.apache.org/userslist.html>  for more info.
To unsubscribe, e-mail: users-unsubscribe@[...].org
   "   from the digest: users-digest-unsubscribe@[...].org
For additional commands, e-mail: users-help@httpd.apache.org