I am using Debian which has Exim4 installed. I changed my /etc/php/apache2/php.ini so it has sendmail_path = /usr/bin/sendmail -t -i
When I do a test message now I get the following error
Message failed! Check your settings and check with your hosting provider
Could not instantiate mail function.
I have full control over this sever so please let me know what configuration changes I need to make to get this working.