Hello,
This is what Extended Notifications is used for. Transaction SWNCONFIG.
You can search on that.
I'm not sure where you're getting your message from. It could be an email step within the workflow or it could be a custom job to look for new workitems. In both cases, it can (and should) be replaced by Extended Notifications.
Check SOST to find out exactly wen these emails are sent and then compare with SWI1 (workflow log) and SM37 (batch jobs) to see where that mail is coming from.
regards
Rick Bakker