Today is the deadline for people to file their federal and state tax returns or to seek an extension for their filings.

Returns must be postmarked with today’s date. Returns that arrive at IRS and state tax offices with later postmarks could incur late filing penalties and interest on any taxes due.

In Maine, the U.S. Postal Service plans to keep certain post offices open later than usual to accommodate late tax filers. None is in Androscoggin, Oxford or Franklin counties.

The main branch of the Portland post office will offer an automated postal center for down-to-the-wire filers.

The customer service window at the Portland post office at 125 Forest Ave. will be staffed and open until 7 p.m. today.

In addition, the office’s self-service lobby will be open until midnight, as will its automated postal center.

The automated postal center allows customers using debit or credit cards to weigh packages and print postage for large envelopes and parcels, up to 70 pounds, then deposit those packages into a secure drop box for shipping. The machines dispense variable rate postage in any denomination for express mail, priority mail, first class, and parcel post domestic mail up to 70 pounds.