Yep, instant sync is never a guarantee. There still has to be a queue for command messages along with authentication plus authorization of said commands. And just like you said, you must be connected to a network that then can reach their cloud to even receive the command queue.

I run a sync service between multiple Active Directory domains as a result of a merger and the directories haven't been cutover yet. Along with this sync is a password sync that is normally instant. Most of the times (> 90%), less than a second. Sometimes 3 seconds. Other times? 2 minutes. Even when things are within the same LAN, there's the possibility of a backed up queue.

So yeah, this is purely on him trusting the sync implicitly and not verifying. In my case, I trust it too but will on occasion have to assist users because it's not infallible. Karma got him and I have zero sympathy.

Nah, it's more like Dropbox. It's a multi-way sync between all devices. Dropbox, Google drive and Microsoft one box all have the same kind of problems. Stuff that's supposed to be deleted ends up not getting deleted, stuff that's supposed to be overwritten ends up getting multiple copies with conflicts Even though nothing else has any changes staged. It's totally possible to do it without all that, but there are cost savings are wrapped up in trying to add intelligence in there to make it communicate with the server less.

I don't really give a rat's ass about the guy cheating, but if a company is going to drag me into their distributed ecosystem I fully expect deleted things to delete everywhere and stay deleted. This isn't the first time that they've been in the news recently for deleted things reappearing.

You can "delete for all" since one or two years, but the Standard has long been "deleting from this device only"

IMAP actually deletes an mail for all the clients.