SPF

   The Sender Policy Framework (SPF) is an email-authentication technique which is used to prevent spammers from sending messages on behalf of your domain. With SPF an organisation can publish authorized mail servers.

Microsoft Office 365

   Microsoft Office 365 is a Software as a Service (SaaS) solution that includes Microsoft Office and other services, such as email and collaboration, from Microsoft’s cloud server. Microsoft Office 365 provides desktop functionalities and is available by subscription.

Viewport - initial-scale

   The viewport is the user`s visible area of a web page. The viewport varies with the device, and will be smaller on a mobile phone than on a computer screen. Before tablets and mobile phones, web pages were designed only for computer screens, and it was common for web pages to have a static design and a fixed size.

Disable Telephone link in HTML on Mobile Devices

   Telephone links are a thing. Like an anchor link you tap to (probably) go to another page, these are links you tap to call a number on a phone-capable device.

No Cache Content

   Forces caches to submit the request to the origin server for validation before releasing a cached copy.

NO Store HTTP Cache-Control

   The cache should not store anything about the client request or server response.