how to setup a url redirect

hello!

we recently moved our server from plesk to virtualmin. so far so good, i'm now experimenting with one site before moving them all. I'm choking on this one issue:

I need to set up a redirection, so that users typing

http://webmail.mydomain.com

be redirected to

https://www.mydomain.com/webmail

So far i failed to achieve it. I tried creating a subdomain and activating the proxy to url.

not only it didn't work, but it breaked the entire server, because of this:

Failed to start service :

Starting web server (apache2)...Warning: DocumentRoot [[/var/www/mydomain/domains/webmail.mydomain.com/public_html]] does not exist Syntax error on line 20 of /etc/apache2/sites-enabled/webmail.mydomain.com.conf: Invalid command 'SSLProxyEngine', perhaps misspelled or defined by a module not included in the server configuration failed!

can you explain me how to do it correctly?

thanks you very much for your time!

Alexandre