Package: bsd-mailx

"bsd-mailx" package binaries on CentOS:

/bin/mail /usr/bin/bsd-mailx /usr/bin/Mail

You may install this package on CentOS with yum install bsd-mailx

"bsd-mailx" package binaries on Debian:

/usr/bin/bsd-mailx

You may install this package on Debian with apt-get install bsd-mailx