To send an announcement on Canvas, you normally use the Announcements tool specific to each course. However, you can also send announcements from your native email app using the external feeds feature on Canvas. To send an announcement via email, set up a dummy blog that supports RSS feeds and posting over email, then link that RSS feed with your Canvas site. The instructions below are for Blogger, but any platform that meets these requirements will work. When finished, you will be able to send announcements to one or all of your Canvas courses, from any email.
Phonologist, lecturer in linguistics, he/him.