I don't know if that helps, but I as a teacher can do so from my postbox in canvas. send to... group a.
But it would be nice to simoultaneously (so + in the receiver-list) write a mail to group a and group c and also to different courses... 🙂
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In the Instructure Community Ideas space, you can share, converse, and rate idea conversations related to software improvements to Instructure products.