If you have been expecting a parcel to be delivered by the PTT, especially one that has been sent using a "signed-for service", it's well worth checking whether it's been intercepted by the Turkish Customs.
The Customs Office (T.C.Basbakanlik Gümrük Müstesarli&gi) is located just inside the harbour entrance, behind the Pasaport Polis offices. It's well worth taking a Turkish friend to help with translation as, although some of the staff speak some English, it'll make it far easier for you.
You will need details of the parcel sender and receiver, an approximate date of despatch, your passport, and if collecting on behalf of a relative or friend, their passport too.
Once the paperwork has been located for the parcel and you have paid any duty levied by customs, you will have to sign the delivery note and you'll then be given a piece of paper that contains details of the package and a unique reference number.
Parcels arriving in Fethiye are randomly checked by the Customs officers. They are taken out of the PTT delivery system and held at Fethiye main post office, not the new sorting office near the Otogar.
On arrival at the PTT in Fethiye, don't go in the front entrance. Go to the right of the building, where the PO Boxes are located, up the 4 steps, through the door and straight ahead through the next door.
This is where you collect your parcel from. You hand-over the paperwork issued to you by customs and your passport. Your parcel will be released to you after signing the necessary paperwork, and paying a 2 TL admin fee.
I was in there yesterday, and there are 30 - 40 parcels awaiting collection.