JACKSONVILLE, Fla. --The deadlines are fast approaching for holiday mail to arrive in time for Christmas, and if you are sending to fleet post offices or air and Army post offices, the post office is your only option.

Katherine Mizla ordered custom made holiday M&M's with a thank you message to send to her neighbor Darius, away from home on a 9-month deployment on the USS Winston Churchill. The Mars candy company failed to deliver.

"They called me and told me they cannot place my order, they only use FedEx for shipping and FedEx will not deliver to FPO or APO addresses. Why commit to just one carrier if that carrier will not deliver to where your customer wants the product to go?" said Mizla.

She was frustrated by the experience.

Only the U.S. Postal Service delivers to fleet post offices or air and army post offices. They are post office boxes controlled by the post office. Milza hopes to still send some kind of care package to the troops, but time is running out.

"In order to get a package to an APO, or FPO, and you are going to ship express mail. The cutoff will be December 17th," said Wendy Fuller of the USPS.

If you use large flat rate boxes at the post office, you'll get a $2 discount for shipments to military members. Just make sure you make the military express mail December 17th deadline and the post office promises to deliver.

"We are going to do our best to get those packages to our loved ones and to ensure they are there safely, securely and ready for them to open with a smile," said Fuller.

If you have a first class letter or card going to anyone this Christmas, you'd better hurry. Those need to be in the mail in just four days, by December 10th, to ensure delivery in time for Christmas.

That includes a letter to Santa in the North Pole if you would like a return letter from Santa.