When I first set up Cain­Manor on slice­host, e-mail wasn’t work­ing. The solu­tion, based on this thread, was to install postfix.

apt-get install post­fix  –Install postfix

edit /etc/postfix/main.cf

mydo­main = cainmanor.com
myo­ri­gin = cainmanor.com
mynetworks_style = host

ser­vice post­fix start –start the ser­vice to see if it works as expected.

chk­con­fig –list post­fix — make sure it will start on boot.  The default install takes care of this