mailCould not instantiate mail function, eform snippet not working

I have a MODx evo install at www.celtictravellingbooks.com, and the contact page enquiry form is showing error

Main mail: Mailer was unable to send mailCould not instantiate mail function.

Am using

[!eForm? &formid=`ContactForm` &subject=`[+subject+]` &to=`[(emailsender)]` &ccsender=`1` &tpl=`ContactForm` &report=`ContactFormReport` &invalidClass=`invalidValue` &requiredClass=`requiredValue` &cssStyle=`ContactStyles` &gotoid=`46` !]

The site hosted on UK2 dedicated server on Linux Server

Any help would be most appreciated, thanks Stewart

Does the PHP mail() function work at all? Have you tested it with an external script?