I think it can be some problem with your WP-Super-Cache plugin, which was configured incorrectly – you can try to ask their support for a solution, because pages loading speed is their business.
Not a solution, but who knows – maybe it can help.
WordPress uses the PHP mail function to send emails generated by WordPress or any third party plugin. However, many WordPress hosting servers are not configured to use the mail function.
Additionally, in order to reduce spam, your email provider often checks whether your email is originating from the location it claims to be originating from. For example, if your email server is yahoo.com but your email claims to be sent from your website’s domain, chances are your form notification will be blocked before it even reaches the spam folder.
