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If you don't see the symbol, it means that you've previously told Google not to use your CNU mail to open mail links and you'll need to reset it.
To reset the mail handler, click on the three dots at the far right of Chrome and choose Settings.
Choose Site Settings.
Click Additional Permissions.
Then, choose Handlers.
Make sure that "Sites can ask to handle protocols" is turned on, and that you don't have anything in "Not allowed to handle protocols". If you do, click the x.
E-mailing your Advisees (each time)
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