Hmm, be cautious. In my experience, there are two common types of non-delivery receipts:

(A) Your mail server quickly tells you a specific recipient's address doesn't exist, mailbox is full, or message was rejected on policy grounds (i.e., it looks spammy)

(B) After several days, your mail server tells you it wasn't able to deliver the message to a specific recipient after numerous retries

What you've described doesn't fit that pattern, so I'm suspicious that it might a phishing attempt to trick you into opening a malicious attachment (which fortunately you cannot see).

Many thanks for your help. I was surprised because when I've had mail returned before I could always find the message I sent. I sent that message to a reliable source at a University which unless its been captured would be unlikely to send rubbish out. I have just sent another message to the same address and it was immediately returned maybe the chap has died and been wiped of the receive list. I will contact the main board there in the morning. Thanks for your help again. Brian

I just checked the address the returned message came from and its the following. "emailsecurity@hes.trendmicro.eu" Does that raise any questions? Brian

Hi Brian, Trend Micro is a security software company. Possibly the recipient's organization uses Trend Micro services to filter its mail, but I would still expect the rejection to come from an address at the recipient's organization. ??