mail()-function doesn't work

Hi, I want to use the mail function, but it doesn't work. In the ini-file is a running and reachable SMTP-server. The from-adress has the right to send via this server. An comparable ASP-scripts with same smtp-parameters works fine. But the call of the php-mail-function results in "Warning: Server Error in c:\webshare\wwwroot\pharma\form_send.php3". The mail-server didn't have logged anything. Which server creates the error? the webserver? the mailserver? And how to get rid of this problem? Thanks Kai