It's a good idea to turn off automatic read receipts.
I got a bogus email purportedly from the ATO yesterday with some malware attached. It was much better written than the usual and they had gone to some trouble to make it look real. Digging through the email headers I found that it originated from an IP address in Indonesia. The malware was only identified by 5 of the 19 scanners here:
http://virusscan.jotti.org/en
If the bad guys get their act together it will be very scary.
Cheers,
Rick.