D'oh!

So, one week wasted chasing down bugs in vpopmail... bleah.
For future reference, causes for:

failure: Sorry,_no_mailbox_here_by_that_name._(#5.1.1)

Remove the recipient domain from /var/qmail/control/locals, otherwise it won't handoff to vpopmail. Wee!

Now I can get back to this stupid error.

success: client_connect:_connect_failed:_2/client_connect:_connect_failed:_2/
tcprules:_fatal:_unable_to_parse_this_line:_Received:_(qmail_7270_invoked_by_uid_1107);
_12_Jul_2010_07:16:24_-0000/did_0+0+1/

And also trying to work out deliveries are being dropped into an empty file in ~/Maildir/ called '-u'.

Yay!