I have moved your post from hereviewtopic.php?f=16&t=20981
as the topic you posted in is now out of date.
You may be using Mercury Mail when you don't need to as the included sendmail application is quite adequate for sending email messages from a php form script, that is, when the sendmail.exe is upgraded and you have configured php.ini and the sendmail.ini files correctly - see below.
Do a forum search in XAMPP for Windows in English for sendmail and you may find that you need to download a fresh version of sendmail if you want to use secure email.
These search results
may help if you are not familiar with searching forums.