Yechiel Michel Dabruskin corresponded with the Rebbe in the 1950s on halachic questions, particularly concerning mikvaos, and on communal matters. No reliable published biography is available; the summary below is drawn from the letters themselves.
Several letters concern mikvaos: changing details in mikveh repairs and following the Rebbe Rashab's instructions for building mikvaos (IK 2135, 3786). Others take up halachic questions: Yom Tov observance for travelers and the Previous Rebbe's practice (IK 2029), Yom Tov Sheni for those moving to Eretz Yisrael, and answering amen in berachos (IK 2089). The Rebbe also wrote on public Torah study and the importance of learning practical halachah (IK 3106), and encouraged him to assist Romanian immigrants (IK 6780).
See also: Marriage – Family purity (taharas hamishpacha) and the mikveh; Halachah and custom – Asking a Rav and halachic questions; Land of Israel – Helping new immigrants settle.