Can someone help me understand this message "packages cannot be authenticated"

[john]

Hi all,

I have an LTSP server running Jaunty. I want to install apticron on
the server.  Apt wants to install an MTA along with apticron which is
fine with me, however
it wants to install postfix AND exim4 and it also warns that the
packages cannot be authenticated. Can someone help me understand why
this might be happening.

Here's the message from APT and below that I've pasted the contents of
/etc/apt/sources.list

Thanks!

John


cbuntu:~$ sudo apt-get install apticron
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following extra packages will be installed:
  apt-listchanges bsd-mailx postfix
Suggested packages:
  procmail postfix-mysql postfix-pgsql postfix-ldap postfix-pcre sasl2-bin
  resolvconf postfix-cdb mail-reader
Recommended packages:
  exim4 mail-transport-agent
The following NEW packages will be installed:
  apt-listchanges apticron bsd-mailx postfix
0 upgraded, 4 newly installed, 0 to remove and 13 not upgraded.
Need to get 1456kB of archives.
After this operation, 3932kB of additional disk space will be used.
Do you want to continue [Y/n]? y
WARNING: The following packages cannot be authenticated!
  apt-listchanges postfix bsd-mailx apticron
Install these packages without verification [y/N]?


$ cat /etc/apt/sources.list
#
# deb cdrom:[Ubuntu 9.04 _Jaunty Jackalope_ - Release i386
(20090420.1)]/ jaunty main restricted

#deb cdrom:[Ubuntu 9.04 _Jaunty Jackalope_ - Release i386
(20090420.1)]/ jaunty main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.

deb http://us.archive.ubuntu.com/ubuntu/ jaunty main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ jaunty main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://us.archive.ubuntu.com/ubuntu/ jaunty-updates main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ jaunty-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://us.archive.ubuntu.com/ubuntu/ jaunty universe
deb-src http://us.archive.ubuntu.com/ubuntu/ jaunty universe
deb http://us.archive.ubuntu.com/ubuntu/ jaunty-updates universe
deb-src http://us.archive.ubuntu.com/ubuntu/ jaunty-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://us.archive.ubuntu.com/ubuntu/ jaunty multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ jaunty multiverse
deb http://us.archive.ubuntu.com/ubuntu/ jaunty-updates multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ jaunty-updates multiverse

## Uncomment the following two lines to add software from the 'backports'
## repository.
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
# deb http://us.archive.ubuntu.com/ubuntu/ jaunty-backports main
restricted universe multiverse
# deb-src http://us.archive.ubuntu.com/ubuntu/ jaunty-backports main
restricted universe multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu jaunty partner
# deb-src http://archive.canonical.com/ubuntu jaunty partner

deb http://security.ubuntu.com/ubuntu jaunty-security main restricted
deb-src http://security.ubuntu.com/ubuntu jaunty-security main restricted
deb http://security.ubuntu.com/ubuntu jaunty-security universe
deb-src http://security.ubuntu.com/ubuntu jaunty-security universe
deb http://security.ubuntu.com/ubuntu jaunty-security multiverse
deb-src http://security.ubuntu.com/ubuntu jaunty-security multiverse