Lesley,
Some years ago, Micheal Campbell will recall this, there was a gardening site here in Ireland where contributions were by e-mail. When a member wrote an e-mail it went to all members, including being sent back to the sender.
One weekend, a member in London, I believe, left her office computer e-mail service set with an automated response - "I am out of the office at present and will reply to your e-mail on Monday". Of course when a message arrived at her computer from the gardening site her computer responded with the automated message back to all members of the site - which returned to her computer and generated another automated response and so on and so on until I had 12,000 in my inbox before my server blocked all messages from her computer.
Paddy