Messages with audio content carry the audio content as a file attachment on the message, in accordance with the procedures for attachment handing as specified in [MS-OXCMSG] section 184.108.40.206. The attachment file MUST be in either the WAV file format (as specified in [WAVE]), the ASF file format (as specified in [ASF]), or the MP3 file format<1>.
If in the WAV format, the audio codec MUST be either G.711 a-law, G.711 m-law, or GSM 6.10, as specified in [G711] and [GSM610]. If in the ASF file format, the codec MUST be either the Windows Media Audio 9 Voice or the WMA 2 codec.
In addition to the common properties on the attachment, the attachment MUST define the following two properties:
PidTagAttachLongFilename ([MS-OXCMSG] section 220.127.116.11): Set to a unique name in the attachment collection of the message. To function properly, the file name MUST be unique for the attachment order logic specified in section 18.104.22.168. The file extension MUST be ".wav" for files in the WAV format, MUST be ".wma" for files in the ASF format, and MUST be ".mp3" for files in the MP3 format.
PidTagAttachMimeTag ([MS-OXCMSG] section 22.214.171.124): Set to reflect the audio content type of the message. The value of the property depends upon how the message is encoded:
For WMA 9 Voice-encoded messages, this value MUST be "audio/wma".
For GSM 6.10-encoded messages, this value MUST be "audio/gsm".
For G.711-encoded messages, this value MUST be "audio/WAV".
For MP3-encoded messages, this value MUST be "audio/mp3".