dropbox.com/s/gk2953l0errp…
H/T @MellaTray for the perfectly timed message that popped into my screenshot
1. Log into One.IU
2. Go to the Faculty Center
3. Set the term/campus to Fall 2020
4. Select the course you want to email
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5. Scroll down past the roster and click 'notify listed students'
6. That will open an email from you to all students in the course.
Thanks @RebeccaLave for this!