I am having this exact problem as well.
I am using on a 5.1b4 box the following:
- ezmlm-idx-std-0.40-2.i386.rpm
- e-smith-ezmlm-idx-0.1.3-19.noarch.rpm
It should work! The ezmlm-make man page has the following for the -u flag (Notice the last paragraph):
-u User posts only. ezmlm-make sets up the list so that
posts and archive access is restricted to sub-
scribers. These are addresses subscribed to the main
list, the digest, or added manually to the address
database in dir/allow/ which accommodates addresses
from e.g. subscribers working from an address other
than their subscriber address.
Posts from unrecognized SENDER addresses will be
rejected. This is relatively easily defeated for
posts. More secure alternatives are message moder-
ated lists configured with the ezmlm-make -m switch
(without the -u switch).
There is no reason to combine of SENDER checks on
posts with message moderation. Therefore, the combi-
nation of the -u switch with the -m switch is used
for a configuration with SENDER restrictions (like
with -u alone), with the difference that posts from
non-subscribers will be sent for moderation instead
of being rejected. This allows the list admin to let
non-subscribers post occasionally, as well as to
catch subscribers posting from non-subscriber
addresses.