Interesting. I only have iMap accounts. I just got an iCloud account and it doesn't say which it is.
Your iCloud account is IMAP.
I have had instances where I didn't get someone's email but that could have been on either end, I guess.
Either end or in the middle. Given all the things that can go wrong it an email, it is amazing to me how much actually gets through. (Often so much gets through I am tempted to wonder if Murphy's law hasn't been repealed — and then an absolutely critical email goes astray...
)