There's a mis-configuration somewhere on Shaw's or Apple iCloud's side. Most emails from Shaw never seem to make it to iCloud. Forwarding emails from shaw to an iCloud address would always return:
550 5.7.1 [CS01] Message rejected due to local policy.
Not sure how to get that fixed.
This is easily replicable by setting up two-factor authentication on my.shaw.ca if you ask for a verification code sent to iCloud.com address, it'll never arrive. If you send it to another email address that forwards it on to iCloud, you'll get the above error message bounced back.
I don't think that "two-factor authentication" makes any difference to your problem, because that option is to prevent any unauthorized person from logging-in to your Shaw ID. That is all that it prevents.
Are you sure that the recipient is not "filtering" E-mail, e.g., accepting E-mail from a short list of IDs, or that the E-mail is being sent to the recipient's "Junk Mail" folder, where the recipient never looks in that folder?
Can you create another ICLOUD ID, without enabling any "filtering", and, if necessary, disabling all "junk-mail-filtering" for E-mail incoming to that ID, and then try to send to that ID?
It’s not the two factor authentication, I was just using that as an example. It happens even with the automated email for this thread.
The attached image is from this morning’s thread response alert.
This happens on other accounts too. I’ve tried with at least 3 other iCloud email addresses over 2 shaw accounts. No filers set, nothing in Junk, and added the shaw email address in contacts.