All,
With the latest change to pambase, e.g.
https://git.archlinux.org/svntogit/packages.git/commit/trunk?h=packages/pamb...
if you have services that rely on pam authentication, such as dovecot, etc.., you will find that your applications an no longer authenticate using pam until you install a specific pam service in /etc/pam.d for that application, e.g.
https://wiki.archlinux.org/index.php/Dovecot#PAM_Authentication
I recall seeing something about this change coming earlier, but this was the first update where something stopped working as a result. So add whatever additional files you require to /etc/pam.d/
Thankfully the journal messages are good in pointing out the problem.