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.

Vary Header check for User-Agent

   When using the Vary: User-Agent header, caching servers should consider the user agent when deciding whether to serve the page from cache

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.

Keep-Alive for 5 secs

   The Keep-Alive general header allows the sender to hint about how the connection may be used to set a timeout and a maximum amount of requests.

LiteSpeed

   LiteSpeed Web Server (LSWS), is proprietary web server software. It is the 4th most popular web server, estimated to be used by 4.7% of websites as of August 2019. LSWS is developed by privately held LiteSpeed Technologies. The software uses the same configuration format as Apache HTTP Server and is compatible with most Apache features.

Gzip Content-Encoding

   The Content-Encoding entity header is used to compress the media-type. When present, its value indicates which encodings were applied to the entity-body. It lets the client know how to decode in order to obtain the media-type referenced by the Content-Type header.