ZhangHuangbin wrote:
iRedMail-0.9.6 works on OpenBSD 6.0, but not 5.9. Our website page is out of date, will update it soon.
Thanks for the quick reply! 
Is it also okay to uninstall PHP 5.x after the install script has finished and then replace it with PHP 7.0? I understand that I will need to update the PHP socket path in the Nginx VHOST configuration.