Last year, the post office handled 180.6 million pieces of international and military mail during the holiday season, Harding said.
Locally, the holiday-related increase in international and military mail is even more significant than the increase in domestic mail, said Hagerstown Postmaster Robert Gingell.
With the post office getting busier and busier as Christmas nears, Gingell said he'd like to see customers get their packages and cards in the mail even earlier than the deadlines.
"We hope that the oversees mailing is taking place as soon as possible," he said.
Missing a deadline doesn't necessarily mean your package won't arrive by Christmas, but the deadlines are the post office's best estimates based on information from its more than 100 partner countries and international shippers, Harding said.
If you miss a deadline and want to make sure your package arrives on time, you can opt for airmail and buy the time for a few more weeks of shopping, Harding said.
Cards and letter automatically go by airmail, she said.
Oversees deadlines for airmail range from Dec. 1 to 8. The military deadline is Nov. 21 for packages and Dec. 1 for cards and letters.
But there's a fair amount of difference in the price of mailing a package surface mail and the airmail price, Harding warned.
For example, it costs almost $5.87 more to mail a 2-pound package to England by airmail than by surface mail. It costs $22.68 more to mail a 5-pound package to Japan by airmail than by surface mail.
"It's enough to make it worth your while to shop early," Harding said.
If you want to take advantage of the lower surface mail rate, be sure not to enclose cards or letters in an international package, she said.
Under Postal Service rules, a package that includes a personal message must be charged at the higher airmail rate, Harding said.