| Platform SDK: Exchange 2000 Server |
[This is preliminary documentation and subject to change.]
Messages are persisted in the Web Store as a MIME-formatted stream, complying with the RFC 822 and MIME specifications, and a set of stock properties defined by a messaging content class such as urn:content-classes:message or urn:content-classes:calendarmessage. Not all properties defined by these classes need be present for each item, custom properties can also be persisted for each item.
Many fields defined for messaging content classes refer to the same underlying message data, but return this data as different data types. For example, every message header field for a Message object can be accessed within the urn:schemas:mailheader: namespace, but all are returned as US-ASCII strings, with any non US-ASCII characters encoded using the mechanism defined in RFC 1522.
Similarly named fields within the urn:schemas:httpmail: namespace, return the same information; in a different data format. Within the urn:schemas:httpmail: namespace, fields are returned as UNICODE characters that is not RFC 1522 encoded US-ASCII character sequences or OLE Automation Date (DATE) variables. Another example is the http://schemas.microsoft.com/exchange/sensitivity field that returns an enumerated value rather than a string identifying the sensitivity of the message. The same relationship exists between properties in the urn:schemas:mailheader: namespace and the IMessage and IBodyPart interface properties. The latter always return UNICODE characters, not RFC 1522 encoded strings.
When accessing fields in the urn:schemas:mailheader: namespace, the underlying OLE DB type for the majority of fields is DBTYPE_STR (a char string). The ADO Fields collection is dual, and therefore oleautomation compatible. Therefore a single-byte characters must be returned as wchar_t (Unicode, or two byte) characters. Non US-ASCII characters encoded per RFC 1522 are not necessarily decoded when returned. The encoding characters remain intact.
urn:schemas:mailheader: Namespace