Exim (v4) is a mail transport agent. this package contains debugging symbols for the binaries contained in the exim4 packages. the daemon packages have their own debug package.

the debian exim4 packages have their own web page, http://wiki.debian.org/pkgexim4. there is also a debian-specific faq list. information about the way the debian packages are configured can be found in /usr/share/doc/exim4-base/readme.debian.gz, which additionally contains information about the way the debian binary packages are built. the very extensive upstream documentation is shipped in /usr/share/doc/exim4-base/spec.txt.gz. to repeat the debconf-driven configuration process in a standard setup, invoke dpkg-reconfigure exim4-config. there is a debian-centered mailing list, pkg-exim4-users@lists.alioth.debian.org. please ask debian-specific questions there, and only write to the upstream exim-users mailing list if you are sure that your question is not debian-specific. you can find the subscription web page on http://lists.alioth.debian.org/mailman/listinfo/pkg-exim4-users