If OSD is already included as an option under the existing service agreement at no extra cost, C-S views messages that remind customers of this unused benefit as a T/RM, as you said. If OSD is not included in the current service agreement--even if it gets the customer a price break--I'd say your emails are subject to C-S. Finally, if the message is transmitted inside your IB system and does not go through the Internet to your customers' public email address, C-S does not apply at all.
_________________________
...gone fishing.