After further investigation things seems to work with sendmail without the WP SMTP plugin. I have also been told by others that the WP SMTP plugin is needed to get email working on Windows hosts and is not needed if running your website on Linux. Hence, I think this was more to do with a specific plugin that to do with my code per se.
I think WP SMTP Mail gives the above behavior for security but I do not know enough about the SMTP protocol to comment further.
Thanks,
nav