I've just received an email from Booking.Com regarding a refund they've offered me on a hotel I'd booked earlier this year. I had to check out 2 days early because the room was full of seagulls. The email contains the line "If you don’t see this email, please make sure it’s not in your spam folder". How does that work then? If I don't get the email, I'm going to reply immediately telling them what time I didn't get it. If you can't see this post, please like it. Ta!
I guess what they're getting at is that most mail clients, devices and stuff like fitness trackers display push notifications so quite often I see I've got an email and the first couple of lines (often similar to those lines you describe) but then when I go to read it it's not in my inbox because one or other spam filter has decided to move it to my spam/junk folder. Far less amusing than your observation, of course. Sorry about that.
I should have known that someone would provide a rational explanation. I should also have known it would be you...