Let's create a CSV file with only the required fields. Let's start with the following steps:

1. Import the csv package:

import csv

2. Create a CSV file with only the required attributes:

with open('mailbox.csv', 'w') as outputfile:
 writer = csv.writer(outputfile)
  writer.writerow(['subject','from','date','to','label','thread'])
    
  for message in mbox:
    writer.writerow([
      message['subject'], 
      message['from'], 
      message['date'], 
      message['to'], 
      message['X-Gmail-Labels'], 
      message['X-GM-THRID']
    ]
  )

The preceding output is a csv file named mailbox.csv. Next, instead of loading the mbox file, we can use the CSV file for loading, which will be smaller than the original dataset.