INT 21 u - LAN Manager Enhanced DOS - DosWriteMailslot
        AX = 5F52h
        BX = class
        CX = length of buffer
        DX = priority
        ES:DI -> DosWriteMailslot parameter structure (see below)
        DS:SI -> mailslot name
Return: CF clear if successful
        CF set on error
            AX = error code
SeeAlso: AX=5F4Fh,AX=5F50h,AX=5F51h

Format of DosWriteMailslot parameter structure:
Offset  Size    Description
 00h    DWORD   timeout
 04h    DWORD   -> buffer

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