[{_id:"should match 1","sequencesPageData":{"mailSteps":[{"mailTemplate":[{"subject":"asdf"}]}]}},{_id:"should match 2","sequencesPageData":{"mailSteps":[{"mailTemplate":[{"subject":"qwer"}]},{"mailTemplate":[{"subject":"asdf"}]}]}},{_id:"should not match 1","sequencesPageData":{"mailSteps":[{"mailTemplate":[{"subject":"zxcv"}]}]}}]

db.collection.find({"sequencesPageData.mailSteps":{"$elemMatch":{"mailTemplate":{"$elemMatch":{"subject":"asdf"}}}}})