Planner or projectmanager is in the lead of the project planning. He or she can share the current planning with the team members. Inside the planning, team members can suggest activities and items (tasks, milestones, meetings, etc.).
The planner or projectmanager can accept the suggestions, everything will happen inside the tool, so there is no need for sending e-mails.
If there is more then one person in charge of the planning, it’s possible to login at the same time with the same username and password.