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2.1.3.4.1.2 Inline Attachments in HTML Messages

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To mark an Attachment object as inline in a message for which the best body text format is HTML, clients do the following:

  1. Set bit 3 (0x00000004) in the value of the Attachment object's PidTagAttachFlags property ([MS-OXCMSG] section 2.2.2.18) to TRUE.

  2. Set the value of either the PidTagAttachContentId property ([MS-OXCMSG] section 2.2.2.29) (preferred) or the PidTagAttachContentLocation property ([MS-OXCMSG] section 2.2.2.29) on the Attachment object. If the PidTagAttachContentLocation property is used, the PidTagAttachContentBase property ([MS-OXCMSG] section 2.2.2.29) MAY be set to fully qualify a relative URI in the PidTagAttachContentLocation property. For details, see [RFC2557].

  3. Clients MAY<79> include a tag that refers to the URI specified in step 2 in the HTML message text. If the PidTagAttachContentId property is used, the URI MUST use the "cid:" scheme.

MIME writers SHOULD NOT<80> rely entirely on bit 0x00000004 of the PidTagAttachFlags property value to be set correctly for all Attachment objects. Instead, MIME writers SHOULD verify all three conditions specified when deciding whether to treat an attachment as inline.