On the surface you might think this is a good idea, but we used this service for sending investor updates. Most of our investors don’t open non-urgent emails within 24 hours. SIB claimed it was some legal requirement.
We switched to Gmass, which sort of hacks your Gmail account to send campaigns. We haven’t had any issue with Gmass blocking our campaigns, so I have doubts SIB was being genuine about the legal requirements.