If you have upgraded your iPhone or iPad to iOS 11 you may encounter issues accessing your McGill email. That's because the Mail app on newly released iOS 11 is currently not compatible with Outlook.com (email on Office 365). If you are still using iOS 9 or iOS 10, you are not affected.
Microsoft and Apple are working together to resolve this issue. In the meantime, they recommend you download the free Outlook for iOS client, available in the App Store. Alternatively, you can avoid updating to iOS 11 until the issue has been fixed.
Find additional information in this article on the Microsoft site.