It's not perfect by any means, assuming you want to reliably send and receive email.
Apple silently discard messages based on their broken content filters.
Members of our ski club mailing list with me.com and iCloud.com accounts don't receive any posts because the footers contain the web site URL:
www.scom.org.uk.
I found all mail containing the phrase scom.org in the body or subject was discarded, whether from or to apple addresses.
It took 2 hours on the phone to support to prove there was a problem and three weeks later it's still not been rectified.
There should be a simple system for reporting false positives.
iCloud email is not fit for purpose.