localhost eddie # emerge sendmail
Calculating dependencies... done!

!!! Error: the mail-mta/sendmail package conflicts with another package;
!!!        the two packages cannot be installed on the same system together.
!!!        Please use 'emerge --pretend' to determine blockers.

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 eddie # emerge -pv sendmail

These are the packages that would be merged, in order:

Calculating dependencies... done!
[ebuild  N    ] mail-mta/sendmail-8.14.0  USE="ipv6 ldap ssl tcpd -mailwrapper -mbox -nis -sasl -sockets" 2,009 kB
[ebuild  N    ] mail-filter/procmail-3.22-r7  USE="-mbox (-selinux)" 222 kB
[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)

Total: 2 packages (2 new, 2 blocks), Size of downloads: 2,231 kB
localhost eddie #