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2.2.3.4.1.4.1 Inline Attachments

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MIME readers SHOULD mark an attachment MIME part as an inline attachment, as specified in section 2.1.3.4.1.2, when they meet the following criteria:

  • The attachment MIME part MUST be a child of a "multipart/related" MIME entity or the child of a "multipart/mixed" MIME entity that is being used to create an aggregate body, as specified in section 2.2.3.3.2.2.

  • The attachment MIME part MUST have a Content-Id or a Content-Location header.

  • The attachment MIME part SHOULD<164> be referenced from an <img> HTML element in the HTML message body.

  • The attachment MIME part SHOULD<165> have one of the following Content-Type header values: "image/jpeg", "image/jpg", "image/pjpeg", "image/gif", "image/bmp", "image/png", or "image/x-png".

Marking attachment MIME parts that do not meet all of these criteria as inline can result in the attachment being hidden from recipients of the message.

A MIME reader MAY<166> set the attInvisibleInHtml flag in the PidTagAttachFlags property ([MS-OXCMSG] section 2.2.2.18) for inline attachments.