Hello everybody,
Thanks for replying so far. It seems like I need just a bit more input

The problems are solved on Virtuemart level, now the website works perfectly on a testserver, but it's not working on the live server. The specs for both are below. Can you tell me if VM calls for any of the functions that my hosting co. has disabled? Or wich functions it calls for before sending the confirmation e-mail?
That would be SO appreciated

Info on the servers (I hope it's sufficient) :
LIVESafe Mode Off
Open basedir None
Display Errors Off
Short Open Tags On
File Uploads On
Magic Quotes Off
Register Globals Off
Output Buffering On
Session Save Path /var/lib/php5
Session Auto Start 0
XML Enabled Yes
Zlib Enabled Yes
Native ZIP Enabled Yes
Disabled Functions pcntl_alarm,pcntl_fork,pcntl_waitpid,pcntl_wait,pcntl_wifexited,pcntl_wifstopped,pcntl_wifsignaled,pcntl_wexitstatus,pcntl_wtermsig,pcntl_wstopsig,
pcntl_signal,pcntl_signal_dispatch,pcntl_get_last_error,pcntl_strerror,pcntl_sigprocmask,pcntl_sigwaitinfo,pcntl_sigtimedwait,pcntl_exec,pcntl_getpriority,pcntl_setpriority,
And probably more that Joomla doesn't have room for to show.Mbstring Enabled Yes
Iconv Available Yes
PHP Built On Linux web02 3.13.0-35-generic #62~precise1-Ubuntu SMP Mon Aug 18 14:52:04 UTC 2014 x86_64
Database Version 5.1.73-0ubuntu0.10.04.1-log
Database Collation utf8_general_ci
PHP Version 5.3.10-1ubuntu3.14
Web Server Apache
WebServer to PHP Interface apache2handler
Joomla! Version Joomla! 2.5.23 Stable [ Ember ] 24-July-2014 14:00 GMT
Joomla! Platform Version Joomla Platform 11.4.0 Stable [ Brian Kernighan ] 03-Jan-2012 00:00 GMT
User Agent Mozilla/5.0 (Windows NT 6.1; WOW64; rv:32.0) Gecko/20100101 Firefox/32.0
TESTSafe Mode Off
Open basedir None
Display Errors Off
Short Open Tags On
File Uploads On
Magic Quotes Off
Register Globals Off
Output Buffering Off
Session Save Path /tmp
Session Auto Start 0
XML Enabled Yes
Zlib Enabled Yes
Native ZIP Enabled Yes
Disabled Functions dl
Mbstring Enabled Yes
Iconv Available Yes
PHP Built On Linux interwebshop.interwebshop.com 2.6.18-348.3.1.el5 #1 SMP Mon Mar 11 19:40:14 EDT 2013 i686
Database Version 5.5.37-cll
Database Collation utf8_general_ci
PHP Version 5.4.25
Web Server Apache/2.2.26 (Unix) mod_ssl/2.2.26 OpenSSL/0.9.8m DAV/2 mod_bwlimited/1.4
WebServer to PHP Interface cgi-fcgi
Joomla! Version Joomla! 2.5.23 Stable [ Ember ] 24-July-2014 14:00 GMT
Joomla! Platform Version Joomla Platform 11.4.0 Stable [ Brian Kernighan ] 03-Jan-2012 00:00 GMT
User Agent Mozilla/5.0 (Windows NT 6.1; WOW64; rv:32.0) Gecko/20100101 Firefox/32.0