Maildir-style mailbox support.
| Function | initializeMaildir | Create a maildir user directory if it doesn't already exist. | 
| Class | MaildirMessage | A message receiver which adds a header and delivers a message to a file whose name includes the size of the message. | 
| Class | AbstractMaildirDomain | An abstract maildir-backed domain. | 
| Class | MaildirMailbox | A maildir-backed mailbox. | 
| Class | StringListMailbox | An in-memory mailbox. | 
| Class | MaildirDirdbmDomain | A maildir-backed domain where membership is checked with a DirDBMdatabase. | 
| Class | DirdbmDatabase | A credentials checker which authenticates users out of a DirDBMdatabase. | 
| Class | _MaildirNameGenerator | A utility class to generate a unique maildir name. | 
| Class | _MaildirMailboxAppendMessageTask | A task which adds a message to a maildir mailbox. | 
Create a maildir user directory if it doesn't already exist.
| Parameters | dir | The path name for a user directory. (type: bytes) |