You can uninstall or removes an installed mail-expire package itself from Ubuntu 14.04 LTS (Trusty Tahr) through the terminal,
$ sudo apt-get remove mail-expire
If you would like to remove mail-expire and it's dependent packages which are no longer needed from Ubuntu,
$ sudo apt-get remove --auto-remove mail-expire
If you use with purge options to mail-expire package all the configuration and dependent packages will be removed.
$ sudo apt-get purge mail-expire
If you use purge options along with auto remove, will be removed everything regarding the package, It's really useful when you want to reinstall again.
$ sudo apt-get purge --auto-remove mail-expire