In Mattermost Jan Kissig mentioned how Authen::SASL::Perl wasn't automatically installed with Koha on a new server. At a glance libauthen-sasl-perl is just a recommendation of libemail-sender-perl, so if for whatever reason recommendations aren't installed, it will fail to install and Koha won't be able to send SMTP emails. We'll need a newer version of Authen::SASL::Perl for bug 38338 anyway, so may as well make it explicit sooner rather than later.