Email sending issues on Win Server 2003 x64

Hi all

I am sure this is an old issue but after googling and reading through these forums I have tried various fixes with no luck. I am getting the dreaded The e-mail could not be sent.
Possible reason: your host may have disabled the mail() function… error and I am running out of things to try.

I have a VPS server through 1and1 and it runs Win 2003 x64 – I have tried the “Install SMTP Config plugin” route with no luck and from what I can see the mail() function has not been disabled in my php.ini.
I have also tried the possible fixes listed here : https://ebestagent.com/wordpress-your-host-may-have-disabled-the-mail-function-error/ with no luck as well.

Could this be an issue related to me using a 64bit Windows ?

Thanks in advance for any help.