[wlug] Exim Install on Ubuntu

Hello all, I've decided to install exim using Ubuntu's Synaptic Package Manager. When selecting some of the packages, some unexpected packages are marked for removal (see below). Marked for installation: exim4, exim4-config ==> automatically marked for removal: postfix, postfix-lts, ubuntu-base, anacron, at, lsb, mailx, mutt Can anyone explain why these are marked to be removed? Thanks, Ivan