[Pkg-exim4-users] dpkg's confiuration phase within the contents of exim4

[Regid Ichira]

  I am trying to get more notion about dpkg's configuration phase within the 
contents of exim4.
I have a running installation, with daemon-light.  I am trying to dpkg -i only 
a newer exim4-base.deb over it.  dpkg tells me that

    dpkg: regarding .../exim4-base_newer-version.deb containing exim4-base:
      exim4-base breaks exim4-daemon-light (<< newer_version)
      exim4-daemon-light (older_version) is present and installed.
    dpkg: error processing /var/cache/apt/archives/exim4-base_newer-version.deb 
(--install):
      installing exim4-base would break exim4-daemon-light, and
     deconfiguration is not permitted (--auto-deconfigure might help)

1. Can you be specific about the dpkg's configuration phase of exim4-base and
  exim4-daemon-light?  Why would deconfiguring exim4-daemon-light might help?
2. Within the contents of exim4, does dpkg configuration phase does more then
  runs the postinst and updates the files listed in the conffiles?