Working with Mail
A follow up flag is a message that appears in a bar that runs across your message header. You know a message has a follow up flag attached when you see a little red flag icon next to it in your Inbox. Click the Flag for Follow Up button on the Standard toolbar in a message window to set a flag. Either the sender, or the recipient, or both, can set a flag.
Using follow up flags is a great way to organize to-do's you get in e-mail. Set flags on incoming messages, then apply the By Follow Up Flag view to your Inbox (or whatever folder you store them in). You can also set a message flag in an outgoing message so the recipient will get a flag and optional reminder.