Since Microblog 2.5 you can select which users can create and reply to microposts.
How to access the permission configuration?
Navigate to Confluence administration > Microblog > Permissions.
Alternatively, click on the settings button in your Linchpin header, then click on the Microblog link. Then choose the Permissions tab.
Permissions configuration
As an administrator, you can choose which users can post or reply inside the Microblog.
Under Permission type you can select the user permissions needed to reply to microposts and to create new microposts.
To choose a permission type, click on the button with two arrows. This will open a drop-down menu.
You can choose between following options:
Add pages
Only users with permission to add pages to a space will be able to create and reply to microposts. This is the default setting.
Add comments
Only users with permission to add comments to a space will be able to create and reply to microposts.
Add blog posts
Only users with permission to add blog posts to a space will be able to create and reply to microposts.