We have a user who sends out emails with delivery reports and read receipts requested on every email.
Intermittently (Around 2 or 3 times a day) they get a message back in Outlook to say the message has been edited and caused conflict. It seems to show 2 read receipts which are exactly the same which the user has a choice of which to keep.
When Keep All is selected, it brings up a message to say there was a problem please try again.
They have Exchange 2010 running on a server in their office and this issue seems to have started when the affected email address was added on to a new starters machine a couple of weeks back although I cant see why having an exchange account on two machines would cause this to happen.
What ever happens with this conflict the email still gets to the recipient. And it only happens on the users machine who had the email originally and not the new user who got the email added recently.
Everywhere else I have looked in to this issue seems to point to an issue with the Blackberry BES, however I am assuered that there are no Blackberry phones within the company and certainly not with this email address on them.