Until recently, your employer was required to mail your T4 slips (reporting your employment income, taxes withheld, etc.). Your employer could provide them by electronic means, but only if you had previously consented.
Effective for the 2017 taxation year – for which T4 slips must be issued by the end of February 2018 – an employer can issue the slips electronically to current employees without their consent, but only through a secure system, not by general Internet email. The employer will not be able to issue a T4 electronically if the employee specifically requests paper copies, or if the employee “cannot reasonably be expected to have access to the information return in electronic format”. These changes were first announced in the 2017 Federal Budget.