localhost log # emerge sendmail
Calculating dependencies... done!
[ebuild  N    ] mail-mta/ssmtp-2.61-r2  USE="ssl -ipv6 -mailwrapper -md5sum"
[ebuild  N    ] mail-filter/procmail-3.22-r7  USE="-mbox (-selinux)"
[ebuild  N    ] mail-mta/sendmail-8.14.0  USE="ssl tcpd -ipv6 -ldap -mailwrapper -mbox -nis -sasl -sockets"
[blocks B     ] mail-mta/sendmail (is blocking mail-mta/ssmtp-2.61-r2)
[blocks B     ] mail-mta/ssmtp (is blocking mail-mta/sendmail-8.14.0)

 * Error: The above package list contains packages which cannot be
 * installed at the same time on the same system.

For more information about Blocked Packages, please refer to the following
section of the Gentoo Linux x86 Handbook (architecture is irrelevant):

http://www.gentoo.org/doc/en/handbook/handbook-x86.xml?full=1#blocked

localhost log # emerge -C sendmail

--- Couldn't find 'sendmail' to unmerge.

>>> No packages selected for removal by unmerge
localhost log # emerge -C ssmtp

--- Couldn't find 'ssmtp' to unmerge.

>>> No packages selected for removal by unmerge
localhost log #