OAR 740-055-0045
OAR 740-055-0045. Determination of Mailing Date
For reports and payments transmitted through the United States Postal Service on which the post-office cancellation mark on the envelope or wrapper containing the report or payment is omitted or is not legible, the department will consider the report or fee deposited in the United States mail as five (5) postal delivery days prior to the date received by the department.