Methods, media, and systems are disclosed for adding new users to a channel in a group-based communication system. The system receives a request to add new users to a channel. The system adds a new user by classifying the new user's email address domain as internal or external. If the domain is internal, the first user is added to the channel as a member, and if the domain is external, the user is prompted for a type of access for the new user. If the new user's access type is guest, the new user is added to the channel as a guest. If the type of access is shared, the channel is shared with an organization associated with the domain, and the new user is added as a member of the channel that has been shared.