Hello Paul, I believe this might be a known issue in some releases of SM. Can you check the current build version and let me know what you're running there? For quicker response you may want to submit a support ticket so we can look into this further. Have a good one!

Hi Kyle,

Version 17 Enterprise, unlimited users.  We recently applied the 7164 update because we were suffering the same spool looping problems others had.  However, this auto-generated delivery confirmation to everyone who sends him emails has been going on since we upgraded to v.17 weeks ago, long before 7164 was applied.

And just to reiterate, it's only affecting a single user, in a single domain, on a server which hosts a great many other domains and users.