[{_id:ObjectId("6890bd4f6cccdcb4b4d4b0c2"),customer_id:"C001",contact:{email:"marla.singer@fightclub.com",phone:"555-1010"}},{_id:ObjectId("6890bda26cccdcb4b4d4b0c3"),customer_id:"C002",contact:[{email:"robert.paulson@fightclub.com"},{phone:"555-2020"}]},{_id:ObjectId("6890bda26cccdcb4b4d4b0c4"),customer_id:"C003",contact:[{email:["narrator@fightclub.com","tyler.durden@fightclub.com"]},{phone:"555-3030"}]}]

db.collection.aggregate([{$project:{customer_id:1,email:"$contact.email"}},{$match:{email:"tyler.durden@fightclub.com"}}])