How to Register for Online Mail
There are three ways to register to receive online mail from the CRA. First, you can enter your email address directly on your tax return, whether you file electronically or by mail. The CRA will automatically register you for online mail.
Second, you can register by telephone. The number to call is 1-800-959-8281.
Finally, you can register online easily by using the My Account service. To do so, log in to My Account and click on Manage Online Mail in the Quick Links bar on the left side of the page. From there, choose the Update Your Current Email address link and follow the instructions.
Once you are finished, you will receive an automatic email from the CRA at the address you entered, confirming that your registration information has been received and that it will be processed within 7 days.