I am using sys-apps/systemd-231. postfix.service runs newaliases in ExecStartPre but also has ProtectSystem=full making /etc read-only.
Same warning, also on systemd unit.
Adding systemd to cc
pull request: https://github.com/gentoo/gentoo/pull/3443
https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=cd5f65de927969d57a211d9af130bb446072a58d commit cd5f65de927969d57a211d9af130bb446072a58d Author: Craig Andrews <candrews@integralblue.com> Date: Thu Jan 12 09:36:39 2017 -0500 mail-mta/postfix: Allow writing to /etc/mail/aliases.db Gentoo-bug: 603458 Closes: https://github.com/gentoo/gentoo/pull/3443 mail-mta/postfix/files/postfix.service | 1 + mail-mta/postfix/{postfix-3.1.2-r1.ebuild => postfix-3.1.2-r2.ebuild} | 0 mail-mta/postfix/{postfix-3.1.4.ebuild => postfix-3.1.4-r1.ebuild} | 0 3 files changed, 1 insertion(+)