I was a Runbox customer for several years and recently switched to Mailbox and never looked back. Runbox is nice, but I had enough of reliability issues, and a few emails got lost.
If I were you, I would use free monitoring services like uptimerobot. There are some other options available. Typically these services provide some basic functionality for free, it would be enough for a small enterprise.
On AWS it is quite easy to create your own external probes for a reasonable price. However, it would require some basic programming skills.
The author has put an offensive banner (https://imgur.com/a/84cuN) in front of his blog page for Russian IP addresses. I just wonder why there is no such thing in the article above