The hypervisor that our VPS runs on ran out of RAM today and the VPS shut down. Unfortunately, no one at the hosting provider seemed to notice or did anything about it. When I realized I had not received any emails all day, I opened a high priority ticket late around 10pm EDT. They migrated us to another hypervisor and restarted the VPS at 10:10pm EDT.
Sorry about the inconvenience if anyone tried to access the site today. I didn't receive my monitoring alerts because my DNS for my email is also hosted on the same server... working on getting them to fix that so it doesn't happen again.