By default an old message remains in your mailbox for 36 hours. To keep a message for longer you can mark a message as Saved. When a Message is saved, the message will, by default, remain in your mailbox for the period that has been set by your system administrator.
To save a message:
Log into your mailbox. For more information, see Logging in.
Press 5 to save a message as you listen to it or after you have heard it.
You hear a confirmation message to tell you that the message has been saved.