I set up an account "a_bob". I put this in the users/assign file:

=a_bob:a_bob:516:231:/home/a_bob:::
+a_bob-:a_bob:516:231:/home/a_bob:-::

I also have a file alias/.qmail-bob with the content:

&a_bob

However, when I send mail to bob@mydomain.com I keep getting a bounced mail
with something like:

<a_bob@domain.com>:
Sorry, no mailbox here by that name. (#5.1.1)

I have other mailboxes/aliases on the same machine and they all seem to work
fine. Does anyone have any ideas or pointers? Thanks.