Have you reported the failed mail deliveries to canvas support? If your messages are set to deliver to your email, and are not there, it could also be that your email is trying to help. I had to turn off an email filtering tool office 365 added that simply hides messages that it determines are less important. Otherwise, forwarding my canvas in box to my email has been pretty effective. I have a rule to put all canvas messages in one folder, and when I reply to them my replies are linked to the matching message in the canvas inbox. Attachments are an exception, however. Attachments will only reach the recipient if you send the message as a canvas message from the inbox. I would hesitate to turn off the feature for that reason. I believe the school can set a default email as the students assigned school email, but students can also update their profile to send them notifications through other methods.
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