Google Groups Question

I have set up several Google Groups which are intended primarily for use as email distribution lists for an organization.  The "owner" of the groups is a gmail address for the organization that I manage (but not my personal address.)  If I want to send an e-blast to one or more of the groups, how do I do that?  Do I send it to GROUPNAME@gmail.com or ?????

It's probably groupname@groups.google.com

Thanks Tom!  (I actually did ... finally ... get the answer, but they didn't make it easy.  Of course, now that I know where it is, it IS easy, but I couldn't find it for the longest time!)

The answer was GROUPNAME@googlegroups.com