@mentions are an easy way to catch someone’s attention and to draw them back into a conversation with a higher priority.
If you cannot @mention someone, it means they do not have a Fleep username or that they are not even Fleep users yet and are participating in the conversation as an email member.
To mention someone, just type the @ character, and a popup menu will appear. If the person's name does not appear in the menu, then you cannot @mention them.
Read more on our blog: Did we mention that we've got @mentions?