E Mail Problem

I've got a problem with e-mails not appear to send.

I've installed TikiWiki via Fantastico and everything appears to be working. I've set it up to require e-mail validation when people register. I've used an e-mail address set up via my HostPapa Control Panel that I have confirmed is sending and receiving e-mails no problem.

I have tried a non-host papa e-mail within TikiWiki and this will send the validation e-mail no problem. So the problem as far as I can see is either with my HostPapa e-mail and something I've not set up properly. Or one of the settings in TikiWiki needs to be changed to make it compatible with my HostPapa e-mail. The two options that are can see are;
- Default Ch#%$!t for sending mail can either be "iso-8859-1" or "utf-8"
- Mail end of line can be either "LF (Some Unix MTA)" or "CRLF (standard)

I've tried every combination of the above but don't seem to have any luck!

Thanks.