Reach for ～をもちまして in formal announcements, ceremonial speech, and business correspondence to mark the point at which something takes effect or comes to an end — closing a meeting, announcing a store closure, an end of service, a retirement date. It is the polite (～まして) form of ～をもって, so it belongs to spoken announcements and written notices addressed to customers or shareholders, never to casual conversation. Because it signals ceremony, it almost always pairs with humble verbs like 終了いたします・閉店いたします・させていただきます.