[Pkg-exim4-users] Problems with Exim4 in Ubuntu

[Ursa Polaris]

   Hello folks! I recently migrated some web and DB systems from some
old machines to new servers in a facility, and everything appears to
have moved over smoothly except my mail services. I migrated from
Debian Sarge to Ubuntu 8.0 and ran a full apt-get upgrade immediately
after install to be up to date. Postfix (blech) was the default MTA
installed, so I promptly ran an apt-get install exim4-daemon-heavy
which installed the heavy exim4 package and all required dependencies.
Here's where things get fun:

I used sudo dpkg-reconfigure exim4-config as usual to setup my basic
MTA prefs; full internet MTA, set my bind addresses, my domains (I
host multiple but all mail for <user> goes to the same user regardless
of domain and that's fine) and told it not to use the split conf
files.

I then copied over my /etc/aliases file from the old server and kicked
exim4 with a sudo /etc/init.d/exim4 restart

Now when I try to send mail to regular user (with no alias, just a
plain account) mail works just fine

When I try to send to an address that has an alias with a :fail:
command it works fine and the fail msg is sent back to the sending
client

However, when I try to send to an alias that redirects mail from one
existing user to another (i.e. root: webmaster) OR when I try to send
to a "real-user" alias (i.e. abuse: real-admin), I get a "550
Unrouteable address" error from exim4.

I have poured over my configs between the old server and the new one,
and I can't find the difference. Is there some tiny setting somewhere
that instructs exim4 to be able to use the "real-user" alias format or
allow a real account to be re-routed to another real account that I
may have overlooked?

Thanks in advance!

- Ursa