How to insert multiple documents at once in MongoDB while skipping documents with duplicate fields

Question

I am using the native Node.js MongoDB driver to insert multiple documents at once. I have an array of javascript objects (where each object represents a user), and I am using the following code.

var col = db.collection('users');
col.insertMany(usersArray, function(err, r) {
    if (err) {
       log('Bulk Insert Error', err);
    } else {
       log('Successful Insert', r.insertedCount);
       db.close();
    }
});

Each user document in the usersArray array has an email field. I do not want to insert objects where a document with the email already exists in the users collection, as I have modelled emails to be unique. Such documents should be skipped in the query.

I know this would be achievable if usersArray had an _id field (where I would use continueOnError: true), but unfortunately my usersArray is from a separate source. Doing single inserts is inefficient, as my usersArray can have well over ~1000 objects.

The work around I have thought of is selecting all documents from db and reconstructing the usersArray with only unique documents in my node application, to reduce the number of requests to MongoDB. Is there a way the collection.insertMany() function can be modified to do this? Raw MongoDB queries will also be appreciated.