What is the output of:
Code:
cat /var/qmail/control/defaultdelivery
Of course you must change the path to the location of the qmail control files in your distro.
If the file does not exist, you have to create it. What you put in that file depends of your imap server. If you prefer ~/Mailbox, then run
Code:
echo ./Mailbox >/var/qmail/control/defaultdelivery