CRA treats a mailed or couriered item as having been received by it five days before the delivery date
S. 248(7) provides that “anything … sent by first class mail or its equivalent shall be deemed to be received by the person to whom it was sent on the day it was mailed.” Be that as it may:
The CRA considers the received date to be the mailroom date (delivered date) minus five days leniency. The CRA strongly encourages the use of electronic filing via certified T2 software.
Neal Armstrong. Summary of May 2019 CPA Alberta CRA Roundtable, General Session – Q.4 under ITA s. 248(7).