How to get users to actually read automated notifications?

Our (large) company is experiencing a problem where certain internal sites will often have maintenance down-time, and employees will often not be aware, causing them to call the web services team, costing productivity for both the employee who didn't expect the outage, and for the employee answering the phone. We currently send out emails (which we found that users tend to automatically delete), as well as posts on the company intranet, however while doing research for an intranet redesign, not knowing when outages will occur is still one of the most voiced complaints.

I've played around with the idea of implementing text-based notifications, which my team is against (forcing the horse to drink when it's not a dire situation), and when I brought up the idea of putting a notification bar on the sites themselves, they came back with the fact that it could get very complicated, as there are many internal sites. I'm wondering if there are any obvious (or not) strategies that I may be missing, that could potentially solve this problem?