What is the defined standard for the structure of an email?

The correct answer is MIME, which stands for Multipurpose Internet Mail Extensions. This standard defines the format of email messages, allowing them to include text in various character sets, as well as multimedia content, such as images, audio, and video. MIME facilitates the embedding of different types of data within a single email message, making it possible for emails to be formatted richly and for attachments to be sent along with the message.

Understanding MIME is crucial, as it significantly expands the capabilities of emails beyond simple text. This has been essential in enabling modern communication, where multimedia content is often an integral part of business and personal correspondence.

Other options refer to different technical standards. AARPA does not correspond to a widely recognized standard for email structure. ICMP, which stands for Internet Control Message Protocol, deals with network communication rather than the structure of email itself. RFC 2100 refers to a particular informational RFC that outlines a framework but does not specifically define the structural format of email, further clarifying why MIME is the appropriate choice for this question.