if delete a mail request receipt without read, the sender will get a automatic unread receipt by exchange server.
this behave is not expected and shown after apply exchange 2010 sp1 Rollup 3 and this is confirmed by MS CSS team.
This is plan to be fix in Exchange server 2010 sp1 rollup 4. But rollup 4 is recalled recently by Microsoft exchange team. Now rollup 4 V2 is released at http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=26910
recently exchange server 2010 sp1 rollup is not good quality because of the recall rollup 3 and 4. Please do not recall rollup 5 this month. Do you think it will be recalled in SEP 2010? Hope this is only a joke.