as some of friends asked me which kind of microphone will work with MX series of Mizuho transceivers and which kind of microphones used Mizuhos originally there I am sharing what I know about it.
For external Mic. need to be inserted the 3.5mm diameter jack plug. See the picture which is available in original manual including the points (6) and (7) regarding the external microphone and external speaker usage.
Hope it helps,
73 - Petr, OK1RP