I was beat with the answere while typeing, but will post anyway. I believe it is changed through some update as well. My admin@domain sends it to my email address so I think your setup was probably correct.
If you go to the /sbin/e-smith/check4updates file, it states "MAILADDR=admin-yum".
If it were to go to admin, it would state "MAILADDR=admin"
Changing "admin-yum" to "admin" should take care of it, however, any subsequent yum updates may change it. SME is template driven.
A more permanent solution would be to make an alias (Pseudonyms from the Collaboration pick on the server-manager menu) called "admin-yum" and have it sent to the Administrator. That way if it ever gets changed to just admin, all you have is an extra alias which is pretty inconsequential in the grand scheme of thngs.
Hope this helps.