Not exactly on the same topic, but I think it's a good story. When my children were little we'd put them into summer camp. I would send an appointment with "something rather summer camp" from my @live account to my wife on her @hotmail account (you can tell the vintage of us by those, but anyhow). By then both of those were running on Exchange infra. I also had a b-dash@microsoft account at Microsoft which was was sure on Exchange, I wanted to block that time on that email. Well, I'd get these bizarre failures to deliver those calendar that were incomprehensible. I eventually tracked it to not liking "summer camp" in subject line. I changed it to "summer lamp" and they went through. !!! Because I was quite connected to Microsoft ecosystem, I was able to file this in proper raid/product studio repo and get it fixed (never sure of the exact reason though), but for years after that my children always went to "summer lamp" because it was funny that way.