And like you say, they do need to prevent their system being used for sending spam. But if they're not going to provide a way for honest parties to avoid sending spam, they need to be reasonable about how they react to spam reports.
I would think sending spam would be more if we allowed people to sign up for a our service and then people used it to send spam.
But these are all internal communications.
They already detect outgoing spam. Good customer service in this case would be to detect that a customer is attempting to send spam and blocking it and potentially notifying them about it.
Sending one and the system might not have detected the spam. It's not visiting the link. But send many at once the system gets curious.