The mail bouncing now works as follows where a user is not matched
either in the alias or the ftpusers file:

1)  If there is no alias file, mail is delivered to any mailbox
	regardless of the ftpusers file.

Or:

2)  If the alias file contains the entry "default deliver", mail is
	delivered to any mailbox regardless of the ftpusers file.

Otherwise:

3)  If there is a default entry, mail is delivered to the mailbox
	specified (which is rechecked for alias expansion).  At this
	stage, if the user on the right-hand-side of the default
	entry is invalid, mail is bounced.

Finally:

4)  If there is no default entry but there *is* an alias file, mail
	is rejected by the SMTP daemon.

