Outlook Express folders Oversized or Corrupted

Problem:
When you try to receive mail in Outlook Express, you can't and you received the following error message:
"An unknown error has occurred. Account: 'your-account-name', Server: 'pop.mail.mail-server.com', Protocol: POP3, Port: 110, Secure (SSL): No, Error Number: 0x800C0133"

This problem usually occurs, due to a corrupted or oversized* "inbox.dbx" file.
*As you might know, the maximum file size of the .dbx files that are used by Outlook Express is 2 gigabytes.
(see: Microsoft's article)