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.

PHP 5.5.30

   PHP: Hypertext Preprocessor is a general-purpose programming language originally designed for web development.

Apache

   The Apache HTTP Server, colloquially called Apache, is free and open-source cross-platform web server software, released under the terms of Apache License 2.0. Apache is developed and maintained by an open community of developers under the auspices of the Apache Software Foundation.

Cache-Control Header Max-Age

   Specifies the maximum amount of time a resource will be considered fresh. Contrary to Expires, this directive is relative to the time of the request. this website is having max-age=3600 secs.

Vary Header Accept-Encoding

   The Accept-Encoding request HTTP header advertises which content encoding, usually a compression algorithm, the client is able to understand. Using content negotiation, the server selects one of the proposals, uses it and informs the client of its choice with the Content-Encoding response header.