To see how many unread messages you have, you can call the list() method from the mailbox object. Use the following code to find out how many unread messages you have:

number_messages = len(mailbox.list()[1])

With this, we just have to loop and get the messages one by one to analyze them:

for i in range (num_messages):
   print("Message number "+str(i+1))
   print("--------------------")
   # read message
   response, headerLines, bytes = mailbox.retr(i+1)

The retr(i+1) method brings the message from the server whose number is indicated and marks it on the server as read. It is set to i+1 because the retr() method starts at 1 and not at zero. This method returns the server response, the message, and a few bytes related to the message that we are reading. The important thing is headerLines, which in some way contains all of the lines of the message.