ReplyBy Time

To generate a Reply-By header, clients set the PidTagReplyTime property ([MS-OXOFLAG] section to the date and time by which a reply is requested. Clients also MUST set the PidLidFlagRequest property ([MS-OXOFLAG] section, as specified in section, to any non-empty string value. If the PidLidFlagRequest property is not set, the Reply-By header will not be generated.

MIME writers SHOULD<57> copy the value of the PidTagReplyTime property to the Reply-By header.