When tracking is enabled, messages arriving in this mailbox have a tracking id inserted into the subject line and a message is returned to the sender informing them that their message has arrived and telling them what tracking number has been assigned to them.
This option is useful for tracking a message. It is most relevant when it is important to keep track of a sequence of replies, e.g. for a technical support enquiry, or sales enquiry. When the group mailbox receives a message the Tracking ID is inserted into the subject along with the date and a three digit number (which increments each time a message arrives in the group mailbox that does not have a Tracking ID in its subject).
It is possible to include special macros into the message. See Macro Expansion