Tax returns must be post marked before midnight Monday to avoid the late filing penalty. The only post office in San Diego County that will remain open until that deadline is the main post office at 11251 Rancho Carmel Drive in the Carmel Mountain area. All other mail collection boxes and post offices will be collected at their normal times, according to the U.S. Postal Service.
People who have not completed their tax returns can avoid penalties by filing for a tax extension, but if they owe taxes, they must include payment for their estimated tax liability.
The Internal Revenue Service estimates that about 5 million tax returns will be mailed Monday.