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

Calculating dependencies ... done!
Dependency resolution took 1.55 s (backtrack: 0/20).

[ebuild  N     ] net-libs/courier-unicode-2.6.0:0/10::gentoo  691 KiB
[ebuild  N     ] net-libs/courier-authlib-0.73.2::gentoo  USE="gdbm pam sqlite -berkdb -debug -ldap -mysql -postgres -static-libs" 2705 KiB
[ebuild  N     ] mail-mta/courier-1.6.0::gentoo  USE="crypt ipv6 nls pam (split-usr) -fam -fax -gnutls -ldap -mysql -norewrite -postgres -spell -test -web -webmail" 8251 KiB
[uninstall     ] mail-mta/nullmailer-2.2-r2::gentoo  USE="ssl -test" 
[blocks b      ] mail-mta/courier ("mail-mta/courier" is soft blocking mail-mta/nullmailer-2.2-r2)
[blocks b      ] mail-mta/nullmailer ("mail-mta/nullmailer" is soft blocking mail-mta/courier-1.6.0)

Total: 3 packages (3 new, 1 uninstall), Size of downloads: 11646 KiB
Conflict: 2 blocks (all satisfied)