Let me tell you about the power of groups in the Elgg. You can send a post just to people in a group you create. You must make people your friend first by clicking on their logo then click make this person my friend. After that, go to Your Network and click Access Controls. Once there, create a group and add people to your group.
Access is controlled through the use of Access groups and this is one of the most powerful features of Elgg. Access groups allow you to have complete control over who sees what within your environment. You can create as many access groups as you wish. Each access group can have as many of your friends as you like and each access group created becomes another option in the 'access restriction' drop-down menu beside each profile item, weblog post and file uploaded.
When you create an access group, add people to it then select it as your access restriction on a weblog post only the people in that group will be able to see that weblog post and so on for all elements in your learning landscape.
A community differs from groups in that anyone can join a community.
Groups is the way to go for select communication. (I use this feature to send messages just to certain classes)
Be aware that in order for you to send a message to a group, you must create a group called on your own and add people to it. A group is not a two way street. It is formed individually from your personal login.
Hope this helps everyone grasp the concept of groups.