[{"_id":{"$oid":"621fbc842ff7d84973d537e7"},"name":"Test","emailAddresses":["email@email.com","email2@email.com","dave@test.com","frank@email.com"],"_class":"com.email.models.Group"}]

db.collection.aggregate([{$addFields:{emailAddresses:{$filter:{input:"$emailAddresses",cond:{"$regexMatch":{input:"$$this",regex:"ema"}}}}}}])