db.save.find().pretty();
{
        "_id" : ObjectId("58884b11e1370511b89d8267"),
        "domain" : "google.com",
        "emails" : [
                {
                        "email" : "f@google.com",
                        "first" : "James",
                        "Last" : "fer"
                },
                {
                        "email" : "d@gmail.com",
                        "first" : "dear",
                        "last" : "near"
                }
        ]
}

C:MongoDBServerbin>mongoexport.exe -d Trial -c save -o file.csv --type csv --fields domain,emails
2017-01-25T12:50:54.927+0530    connected to: localhost
2017-01-25T12:50:54.929+0530    exported 1 record

domain,emails
google.com,"[{""email"":""f@google.com"",""first"":""James"",""Last"":""fer""},{""email"":""d@gmail.com"",""first"":""dear"",""last"":""near""}]"

> db.sir.find().pretty()
{
        "_id" : ObjectId("5888529fa26b65ae310d026f"),
        "domain" : "google.com",
        "emails" : "[{"email":"f@google.com","first":"James","Last":"fer"},{"email":"d@gmail.com","first":"dear","last":"near"}]"
}