Sending emails

Hi guys,

I'm building a website using C.I 3 and have like 3 different forms for different pages (career, quote and contact).
The contact form works very well and I do receive emails but the remain two (career and quote) prompts an error whenever I try it (Unable to send email using PHP mail(). Your server might not be configured to send mail using this method) while they are all under the same controller. I don't really know what the problem is.  Can anyone help me solve this issue please?
below is the link to my source code:

http://pastebin.com/REFjPsUf

Thanks