Reading package lists... Done
Building dependency tree
Reading state information... Done
Package mailx is a virtual package provided by:
  mailutils 1:2.1+dfsg1-4ubuntu1
  heirloom-mailx 12.4-1.1
  bsd-mailx 8.1.2-0.20090911cvs-2ubuntu1
You should explicitly select one to install.
E: Package mailx has no installation candidate