“welcome to my hometown” virus

We have received an email from one of our clients notifying us that we sent out a message with the welcome to my hometown subject. He sent the message back to us asking how to open it. It looks like it was sent out by our postmaster. He has received two of these messages, but nobody else has received any. Can anyone tell me more about this virus? Would this message have to come from us or could it be generated elsewhere? Thanks!