To make sure that your support, billing and other emails direct the customer to your WordPress site instead of directly to your WHMCS site, you need to install and activate the WHMCS Bridge Helper addon which is included in the Pro version of WHMCS Bridge.

Just set the URL in the addon settings to the URL of your WordPress Bridge page and customers visiting your WHMCS site directly will be redirected to your WordPress bridged WHMCS page.