I'm getting this on my own website too. I've written my own php mail script for the contact form so I presume they are using that.
The e-mails are random though. And are more like
hjfdhjkh@munkyonline.co.uk and the subject will be jkldjfklsfjkl too!
It seems to have died down a bit now but I was getting at least four e-mails a day!
I think someone said that people use this to somehow gain access through frontpage extensions on the server. I dont have this as my website is hosted on a Linux server so thats probably why they're starting to give up?!