db={students:[{_id:"67264264726476",name:"abc",email:"student1@email.com"},{_id:"67264264726477",name:"def",email:"student2@email.com"},{_id:"67264264726478",name:"xyz",email:"xyz@email.com"}],followups:[{_id:"65536854685",student:"67264264726476",message:"This is a student follow up"},{_id:"65536854686",student:"67264264726477",message:"This is a student follow up"}]}

db.followups.aggregate([{$lookup:{from:"students",localField:"student",foreignField:"_id",as:"student",},},{$unwind:{path:"$student"}},{$match:{$or:[{"student.name":{"$in":["abc","def"]}},{"student.email":{"$in":["xyz@email.com"]}},],},},])