If emitting via email, it will send from yum-updatesd.com.
Which is totally invalid for two distinct reasons.

#1 The address yum-updatesd@ is invalid. Use a valid user like root or create an
alias.

#2 Host should already have a name. In this case, it is bozo.example.com. And a
properly configured mailer already knows it's name. So the @localhost needs to
be removed entirely. Of course just using @localhost. (with trailing dot) would
be valid too, although less preferred.

Workaround:
email_from=root
email_to=root