Some correction and added informations:
CORRECTION:
The messages are NOT generated by your ISP or webmail provired.
The messages are generated by the server on the recipient side.
ADDITIONAL INFO:
If it's NOT in response to some e-mail you sent, then the most probable cause is as follow:
The computer of somebody, somewhere in the world, is infected by a virus and used to relay SPAM.
Your address have been harvested somewhere.
The virus puts your e-mail address in the "From:" field and possibly also in the "Reply to:" field.
At least some of the spamed addresses are fake or no longer active.
Final word: There is nothing you can do to stop those automaticaly generated, and legitimate, information messages.
You can set filtering rules to place them is a special folder or delete them.
Electro
July 2011