The CRA is merging the Online mail and Account alerts services
Source: Canada Revenue Agency
The CRA is merging the Online mail and Account alerts services to create an improved email notification service for Canadians. Beginning January 3rd, 2019, the CRA will email users to inform them of this change. Go to protect yourself against fraud for help identifying fraudulent emails.
This change will take effect on February 11th, 2019. If you are currently registered for either Online mail or Account alerts you will automatically be registered for the new email notifications service. If you don’t want to be registered for this new service, log in to My Account and remove your email address before February 8th, 2019.