It is sometimes the case that mail cannot be delivered because the mailbox to which the message is addressed does not exist on the relevant system.
User mailbox names on central systems at the University of Cambridge normally consist of a sequence of letters followed by a sequence of digits. A common error is to confuse the digit "1" (one) with the letter "l" (el). Similarly the digit "0" (zero) and the letter "o" (oh) can cause confusion. Please check that you have not made an error of this type in the address you are using.
The search page contains the means of finding people at Cambridge University.
If you receive a bounce from a message that you did not send, this is probably because the original message was forged. This is a common tactic of viruses and spammers, so these bounces are known as "collateral spam". Unfortunately, Internet email has no way of guaranteeing that a message was sent by the person it appears to be from, so the only thing you can do with collateral spam is simply delete it.
If you need further assistance, please email email@example.com, giving as much information as possible. Please note, however, that in order to comply with the Data Protection Act 1998, we can only supply email addresses to a third party if we have been authorised to do so.