In Gmail, you can do all this with a task that links to an email message. These are easy to create, too, starting from the message in question.
Create a Task from an Email in Gmail
To create a new to-do item from and linked to an email message in Gmail:
- Open the desired conversation or check it in the message list.
- Press Shift-T.
- You can also click More Actions and select Add to Tasks.
- Click in the task description to edit the default (the message's subject).
- Now you can move the task or make it a sub-task of another task. Sub-tasks also let you link a single task to multiple messages.
To open a the message related to a to-do item in Gmail Tasks:
- Click Related email in the task list for the desired task.
To remove an email association from a to-do item in Gmail Tasks:
- Highlight the desired task (click anywhere in its title, for example).
- Press Shift-Enter.
- Click the x next to Related email.