What is the difference between mdbox and Maildir?

Question

What is the difference between mdbox and Maildir?

Answer

Maildir is an older mailbox format that stores each email message as a file in the mailbox's folder. This allows individual emails to be modified, deleted, or added without affecting the mailbox or other emails in the account.

mdbox is a high-performance mailbox format that stores all email messages in a single file in each mailbox's folder and indexes the messages.

Additional resources

Maildir Mailbox Format

dbox Mailbox Format: mdbox (Multi-dbox)