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

Calculating dependencies ... done!
Dependency resolution took 1.52 s (backtrack: 0/20).

[ebuild  N     ] mail-mta/msmtp-1.8.33::gentoo  USE="filecaps gnutls mta nls ssl -daemon -doc -idn -keyring -sasl -verify-sig" 453 KiB
[uninstall     ] mail-mta/nullmailer-2.2-r2::gentoo  USE="ssl -test" 
[blocks b      ] mail-mta/nullmailer ("mail-mta/nullmailer" is soft blocking mail-mta/msmtp-1.8.33)
[blocks b      ] mail-mta/msmtp[mta(+)] ("mail-mta/msmtp[mta(+)]" is soft blocking mail-mta/nullmailer-2.2-r2)

Total: 1 package (1 new, 1 uninstall), Size of downloads: 453 KiB
Conflict: 2 blocks (all satisfied)