HELP NEEDED No User registration confirmation mail

For some unknown reason, Hikashop is not sending registration confirmation e-mails anymore. So my clients can't register anymore as they are not able to activate their account. Please help.

HikaShop sends the confirmation email using joomla.
If emails are not sent, maybe that's because you changed the email settings in Joomla ? Or something changed on your hosting company email server.

hmm, I get other mails from the specific e-mail address, so the hoster can't be rep for this issue. Can oyu point me to the place where to change e-mail settings in Joomla. Maybe the problem is there...

Is there a chance to change the registration, so that customers do not have to wait for the confirmation e-mail to activate their accounts but have the account activated right away?

Sure, if you don't want the registration to have an activation email, you can just turn off the corresponding option in Joomla. That option is in the configuration of joomla 1.5 and in the options of the user manager on joomla 1.6 and 1.7.
The email options of joomla are in the configuration of joomla.