The U.S. Postal Service is advising Hawaii residents and businesses to mail First-Class and Priority cards and packages to the mainland no later than Dec. 18 this year for delivery by Christmas.

Other suggested mailing dates are Dec. 10 for international or overseas military destinations, Dec. 13 for American Samoa, Dec. 14 for Guam and Saipan and Dec. 20 for Hawaii destinations, the Postal Service said Monday.

 Procrastinators have until Dec. 20 to send packages to the mainland with expedited Express Mail service.

The Postal Service said the dates are not deadlines, and that mail sent after those dates could still arrive by Christmas. The suggested dates, however, give packages the best chance of arriving on time, the Postal Service said.

The agency also said:

>> The Honolulu Airport post office will be open an additional day to serve customers, on Sunday, Dec. 16 from noon to 5 p.m.

>> Postal carriers on city routes will deliver parcels on two Sundays, Dec. 16 and 23.

>> Eighteen Hawaii post offices have self-serve kiosks at which customers can buy stamps and send packages. On Oahu they are at the Aina Haina, Airport, Ala Moana, Downtown, Hawaii Kai, Kailua, Kaneohe, Makiki, Mililani, Moiliili, Waialae-Kahala, Waikiki and Waipahu post offices. On the neighbor islands they are at the Hilo, Kailua-Kona, Kihei, Lahaina and Wailuku post offices.

>> People can get online discounts on postage, print mailing labels and arrange for free parcel pickup at usps.com.

>> The Postal Service anticipates delivering almost 18 billion pieces of mail between Thanksgiving and Christmas this year.

>> The busiest mailing day is expected to be Dec. 17. The busiest delivery day is likely to be Dec. 19 for cards and letters and Dec. 20 for packages.