The EnableSendRawUnicast setting is new in V1.9.1.
[Settings] EnableSendRawUnicast=0 ; Default : 0
The DHCP protocol allows the client to specify a broadcast flag. If this flag is not set, then the DHCP server is asked to unicast the response. Unfortunatly, there is no standard mechanism based on the winsock programming interface that would allow the DHCP server to send unicasts solely based on mac address addressing scheme. In V1.9.1 the usage of the winpcap library got implemented. In situations where a unicast is required without having an IP address of the client at hand, the wpcap.dll function pcap_sendpacket is used. The EnableSendRawUnicast setting enables this functionality. Please set to 1 only if there are really problems with clients in that situation. Clients actually should be also fine with receiving responses as broadcast, which is the default behavior if EnableSendRawUnicast is not set or the wpcap dll is not installed. This has been tested with winpcap Version V4.1.1. Please also see the description of the OverwriteBroadcastFlag setting for even more advanced options to set.