amiond wrote:I dont know how to setup mercury to use the mail server on my webhotel
If there is already a mail server on your webhotel (whatever that means), you dont need to setup another mail server (like Mercury), instead use that existing mail server. Anyway, it is not an easy job to setup a mail server (we cannot give support on that), there is plenty of documentation about Mercury. But mostly all that work is in vain, because emails coming from "private" mail servers (i.e. a PC at home or similar) usually never arrives, as all big players (like GMX etc.) are blacklisting private IPs due to SPAM problems.
You should go for an official SMTP Server (like GMX, Google etc.) or from an official Webhoster (where you also can host your site). Everything else wont be usefull.