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Mime stands for Multi-Purpose Internet Mail Extensions. In its original version, it defined certain types of email attachment data so that these files could be read and executed when they were not in ASCII format. The MIME specifications include various multimedia formats such as image files, video, text, and numerous application formats.

General information

MIME has proven to be above all useful in the treatment of data types and is no longer used solely as a reference to the format of an email attachment. The MIME specifications have been established as standard in the field of Internet protocols. The reason is that specific metadata is transferred with every dialogue between a client and a server. MIME establishes an important part of this metadata that is found in the header of an HTML document. Both the server and the browser will then know what kind of data to transmit and basically read or execute.

MIME types are specified as standard by IANA, which is an organization that deals with IP address assignment and other Internet standardization issues.

Practical relevance

If you open an email that contains images, these images can be viewed directly thanks to the MIME types. Because if the data type is defined, for example, with the GIF format for images, the email program will be able to know how these files are handled. The beginning is equivalent to a dialogue between client and server. The servers transfer MIME data at the beginning of each session. Browsers obtain from the MIME data of the header the app to be used for the data type in question. Some apps are already integrated into the browser, but others must be loaded externally. If there is no application to run the file, the file is basically downloaded for later use or a recommendation is given for an appropriate program.

HTML documents also contain items that identify a MIME data type as the value of an attribute. Examples include links, scripts, and parameters. A data type can be set with the attribute "type". It is also feasible to define your own data types with MIME, if these are not already in the IANA standard.[1]

The MIME type schema is established as part of the Internet Engineering Task Force (IETF) Request for Comments (RFCs). Each MIME type is about the specifying a media type and a subtype. A slash separates the two types of information.[2] For example: text / html, image / gif, or application / mspowerpoint. Subtypes for server-side file formats are introduced with the preamble "x.". There are the following types of media:

  • text = for text files
  • image = for graphic files
  • video = for video files
  • audio = for sound files
  • application = for program dependent files
  • multipart = for multipart data
  • message = for messages
  • model = for complex files

Relevance for SEO

Search engine algorithms are always trying to read the entire content of an HTML document. A few years ago they still couldn't track file formats like images, videos, or podcasts. Even though search engines cannot read the entire content of MIME data types, they at least know what data types can be found in the document in question, and therefore have a indication as to content. At the same time, additional metadata can be passed to a search engine's user agent, making it clear how the content is ranked.

Nowadays, all search engines are working to make more types of crawlable data. PDF documents or PowerPoint presentations are no longer an obstacle. If you are looking to load certain types of data on the server or the client, it is recommended from an SEO perspective to pass the respective MIME type with the document header.

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