Вы можете повторить значения и проверить значение.
var listOfPeople = { 0: { referred: [], _id: "5e177e40f3f68644b72e1f14", email: "e@w.f", __v: 0 }, 1: { referred: [], _id: "5e147e90f3f61644b72e1f75", email: "d@ds.d", __v: 0 }, 2: { referred: [], _id: "5e177eb2f3f68344b72e1f76", email: "d@fj.s", __v: 0 }, 3: { referred: [], _id: "5e172f32f3f48644b74e1f77", email: "j@dfhgh.cg", __v: 0 }, 4: { referred: [], _id: "5e177f46f3f68444b72e1f78", email: "jhvg@df.cg", __v: 0 }, 5: { referred: [], _id: "5e1781baf3f68214b72e1f79", email: "test@rest.com", __v: 0 } },
find = "d@fj.s",
result = Object.values(listOfPeople).some(({ email }) => email === find);
console.log(result);