To generate a Subject header, clients SHOULD set the PidTagSubjectPrefix property ([MS-OXOMSG] section and the PidTagNormalizedSubject property ([MS-OXCMSG] section on the Message object. Clients MAY set the PidTagSubject property ([MS-OXPROPS] section 2.1023) instead, but in that case, the separation of the subject from the subject prefix is vulnerable to limitations of the server's parsing procedure, as specified in section The values of the PidTagSubject and PidTagNormalizedSubject properties SHOULD NOT contain line breaks.

MIME writers SHOULD generate the Subject header by combining the values of the PidTagSubjectPrefix and PidTagNormalizedSubject properties. MIME writers MAY<36> instead copy the value of the PidTagSubject property ([MS-OXCMSG] section to the Subject header.

If those two properties are not available, MIME writers MUST copy the value of the PidTagSubject property to the Subject header. MIME writers MAY truncate the subject value. The property value SHOULD NOT be truncated in the middle of a multiple-byte character.

When generating a TNEF message, MIME writers SHOULD<37> also copy the message subject (however it is obtained) to the attSubject attribute, as specified in [MS-OXTNEF] section, and the attMsgProps attribute, as specified in [MS-OXTNEF] section MIME writers SHOULD also copy the PidTagSubjectPrefix property, with its value, to the attMsgProps attribute.