The default config file for yum-updatesd does not send out any email messages  
at all, due to 2 missing variables in the config file.

Here is a working version for you to tweak for your system. This is an issue 
that really needs to be fixed - ie the email_to & email_from properties need 
to be added to the default config file. Then users will be able to see what 
values they need to set for their system, to receive the email notifications 
for available upgrades.

[main]

# how often to check for new updates (in seconds)
run_interval = 3600
# how often to allow checking on request (in seconds)
updaterefresh = 600

# ------------------------------------------------------

# how to send notifications (valid: dbus, email, syslog)
emit_via = email

# who to send the email notifications to
email_to = keith@karsites.localdomain

# who sent the notifications
email_from = root@karsites.localdomain

# ------------------------------------------------------

# automatically install updates
do_update = no
# automatically download updates
do_download = no
# automatically download deps of updates
do_download_deps = no

# ------------------------------------------------------
# eof

Even with this working config file, yum-updatesd only seems to run 
occasionally. I'm aware of the bug reports in general about yum-updatesd.

I'm considering stopping and restarting yum-updatesd with a root cron job, to 
see if that will force yum-updatesd to check for updates.