There is a lot of other dependencies to declare other than postfix, MTA
would have been better.

I agree, and suggest to open an RFE on ovirt-host (and elsewhere?
didn't check) to change the Requires:.


ovirt-host have a lot of dependencies:
rpm -q --requires  ovirt-host        
NetworkManager-config-server
cockpit
cockpit-dashboard
cockpit-machines-ovirt
cockpit-networkmanager
cockpit-ovirt-dashboard
dracut-fips
firewalld
glusterfs-rdma
ipa-client
katello-agent
mailx
net-snmp
net-snmp-utils
ovirt-host-dependencies = 4.2.3-1.el7
ovirt-hosted-engine-setup
ovirt-provider-ovn-driver
postfix
python-firewall
rng-tools
rpmlib(CompressedFileNames) <= 3.0.4-1
rpmlib(FileDigests) <= 4.6.0-1
rpmlib(PayloadFilesHavePrefix) <= 4.0-1
screen
sysstat
tcpdump
vdsm-hook-ethtool-options
vdsm-hook-fcoe
vdsm-hook-openstacknet
vdsm-hook-vfio-mdev
vdsm-hook-vhostmd
vdsm-hook-vmfex-dev

Many of thee are useless depending of your setup.
rng-tools, for example, but my hardware don't provides any of the needed random generators.
screen, tcpdump ? I'm quite surprised.
glusterfs-rdma, I'm not doing glusterfs, and I don't have any hardware to do rdma