user agent (UA)
- A user agent(UA) is a functional instance of an MHS system, e.g. according to X.400. In other mail systems they are called mail user agents( MUA). The user agent is a service provider that makes the services of the message transfer service( MTS) available to the user in an optimal form. As an application process, it enables the user to create, send, receive and, if necessary, archive messages. The User Agent communicates directly with the user and the Mail Transfer Agent ( MTA) of the Message Transfer Service (MTS).
- In Hypertext Transfer Protocol( HTTP), the User Agent forms the Web client, or Web browser, which communicates with the Origin Server, the Web server, using the request- response method. The user agent sends a request to the web server and receives a response message in return.
- In search engines, user agents are programs that query search engine data. User agents thus include spiders, robots and crawlers. The user agents have their own identifier, which is transmitted in the header of the HTTP protocol when a web page is requested.
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