This behavior is a feature of Exchange 2007. This feature helps ensure that the sender who requests a read receipt receives an acknowledgement that the mail was downloaded to the recipient's mailbox. This feature also provides the sender with an additional acknowledgement when the recipient opens the message and clicks OK in the dialog box that asks them if they want to send a read receipt.

In Exchange 2007, the behavior of this feature cannot be modified for clients that use the POP3 and IMAP4 Internet protocols. There are no client or server configuration settings that can be changed so that only one read receipt will be sent.

However, if your users must use the read receipt feature, you can avoid the sending of duplicate read receipts by having your Exchange clients that are using POP3 or IMAP4 use an alternative client to connect to their Exchange mailboxes. One way to avoid the duplicate read receipt messages is to have your POP3 and IMAP4 clients connect to their mailbox using an Exchange e-mail account through Microsoft Office Outlook. Another way to do this is to have your users who currently use POP3 or IMAP4 switch to using Microsoft Outlook Web Access. When users who are using an Exchange e-mail account or Outlook Web Access use the return receipt option, only one read receipt is sent, when the mail is read by the recipient.

Your users who are not using Outlook Web Access or Outlook may be able to avoid being sent duplicate read receipts. To do this, they should try to turn off the read receipt feature from inside the e-mail application they are using.