Hello,
Thanks for your Patience!
So we have been already working on this and trying to make this work properly with Gmail OAuth and additionally, we want to make this easier for our Canvas Users but it is way too complicated to setup. Currently, we do not recommend you to use Gmail for sending Emails especially because of this unnecessarily complicated setup.
We highly recommend using MailGun or SendGrid (they have completely free plans) and they are very secure to use and super easy to setup. Just a Few DNS Settings and the complete setup takes just within 5 minutes. Please consider trying them out.
Hope this Helps!
Let us know if we can help you with anything else or if you find any further issues.