User B enables the "Tell me when all messages have been read" tracking option in Outlook. This option notifies the message sender that the message has been opened by the recipient, including date and time.
(To do this, on the Tools menu, click Options, click E-Mail Options, click Tracking Options, and click to select the Tell me when all messages have been read check box.)
User B sends a message to User A.
User A doesn't read the message (the delegate, User D, does), hence the following message tracking notification to User B:
-----Original Message-----
From: User A
Sent: Friday, March 12, 1999 12:18 PM
To: User B
Subject: Meeting
Your message
To: User A
Subject: Meeting
Sent: 3/12/99 12:18 PM
was deleted without being read on 3/12/99 12:18 PM.
The delegate, User D, selects the option to delete meeting requests after they've been accepted, or simply deletes the request after it is processed.
(To do this, on the Tools menu, click Options, click E-Mail Options, click Advanced E-Mail Options, and click to select the Delete meeting request from inbox when responding check box.)
Enabling this setting removes a meeting request from the Inbox when User D responds. If User D accepts the meeting request, the meeting is entered in the Calendar.