exim是一款常見的郵件發送軟件, 用自帶的apt-get安裝的exim4版本是不支持DKIM，我們必須要對其源碼進行改造才行。

    這里介紹一下在debian環境下對exim進行DKIM（DomainKeys Identified Mail）郵件簽名的支持。

# apt-get install libdkim-dev dpatch
在/etc/apt/sources.list中添加：

deb-src http://ftp.us.debian.org/debian lenny main contrib non-free
添加必要的軟件：

# cd /usr/src
# apt-get --force-yes -y install build-essential devscripts docbook-xsl xsltproc docbook-xml libpcre3-dev libldap2-dev libpam0g-dev libident-dev libdb4.6-dev libxmu-dev libxt-dev libxext-dev libx11-dev libxaw7-dev libpq-dev libmysqlclient15-dev libsqlite3-dev libperl-dev libgnutls-dev libsasl2-dev
# apt-get source exim4
# cd exim4-4.69/
# fakeroot debian/rules unpack-configs
然后復制配置文件

# cp EDITME.exim4-heavy EDITME.exim4-custom
# echo "EXPERIMENTAL_DKIM=yes" >> EDITME.exim4-custom
# echo "LDFLAGS += -ldkim" >> EDITME.exim4-custom
# fakeroot debian/rules pack-configs
修改
vi debian/rules
找到extradaemonpackages這行，修改為：
extradaemonpackages=exim4-daemon-heavy exim4-daemon-custom
為了讓exim找到libdkim，還需要

echo "80_libdkim_patch" >> debian/patches/00list
cd debian/patches
wget 'http://bugs.debian.org/cgi-bin/bugreport.cgi?msg=5;filename=99_libdkim_1.0.19.dpatch;att=1;bug=486437' -O - | \
  cat >> 80_libdkim_patch.dpatch
完成以上步驟，并無提示出錯i后就可以編譯了

debuild -uc -us
之后就可以得到安裝包了：

# ls ../*.deb | grep exim4
../exim4_4.69-7_all.deb
../exim4-base_4.69-7_amd64.deb
../exim4-config_4.69-7_all.deb
../exim4-daemon-custom_4.69-7_amd64.deb
../exim4-daemon-custom-dbg_4.69-7_amd64.deb
../exim4-daemon-heavy_4.69-7_amd64.deb
../exim4-daemon-heavy-dbg_4.69-7_amd64.deb
../exim4-daemon-light_4.69-7_amd64.deb
../exim4-daemon-light-dbg_4.69-7_amd64.deb
../exim4-dbg_4.69-7_amd64.deb
../exim4-dev_4.69-7_amd64.deb
../eximon4_4.69-7_amd64.deb
安裝包的順序
dpkg -i exim4-config*.deb
dpkg -i exim4-base*.deb
dpkg -i exim4-daemon-light*.deb
dpkg -i daemon-custom*.deb
，修改配置文件/etc/exim4/exim4.conf.template在remote_smtp 處
添加：

dkim_selector = dkim
  dkim_domain =  ${lc:${domain:$h_from:}}
  dkim_private_key = /root/dkim.private.key
  dkim_strict = 0
  dkim_canon = relaxed