The British Forces Post Office is having to adapt to new rules and regulations because of Brexit.
The withdrawal agreement is affecting overseas personnel and their families in the European Union (EU) receiving goods ordered from the UK.
HMRC is now working to smooth the process in all countries, including Germany, where the impact is being felt.
In Cyprus, postal arrivals over a certain value are now subject to Cypriot VAT or duties, as the Sovereign Base Areas on the island remain in the EU customs territory, unlike the UK.
Packages arriving on aircraft at RAF Akrotiri were previously taken to an office a few minutes from the base, but are now sent to a warehouse in the port in Limassol – several miles away.
Parcels and packages are only released once officials figure out their value, and whether or not a fee is payable.
Chief of Logistic Operations, British Forces Cyprus, Lieutenant Colonel Steve Jermy, told Forces News: "We always knew, when we started this process almost two years ago in the planning, that... there were going to be changes to parcel post. They are now manifested.
"We have tried to message that as best we can. Some of that messaging needs to be improved and we recognise that. Some of our behaviours as customers need to change and how we use the process."
Neil Furber, senior revenue officer at The Fiscal Office, Headquarters Sovereign Base Areas Administration, said: "If a parcel arrives and it’s less than €17 and nine cents, under the low-value purchase scheme, there’s no tax and duties due on it.
"From €17 to €150 – you pay VAT, usually 19%. There is 5% on some items, but it’s generally 19% VAT.
"Anything over €150, we then have to factor in import duty as well."
Fewer than half of the parcels arriving so far have had customs declarations on them.
Customers were initially being asked to fill out an online form to declare what they were receiving, but that process was scrapped after a few weeks.
The lack of declarations is creating "significant challenges", according to Mr Furber, who said negotiations are ongoing with the Republic of Cyprus about how the procedures will be adopted.
He said UK retailers "just don’t get" that the parcels are being exported as they are being sent to a UK address at RAF Northolt, and then being sent abroad.
Mr Furber suggested retailers be informed about the process, to put customs declarations on and not charge VAT.
Despite the new rules, however, it has not put people off ordering things from the UK.
Lt Col Jermy told Forces News: "We have had approximately at least double the amount of mail that we would normally have at this time of year."
In a message for those considering ordering parcels from the UK, Lt Col Jermy said: "Make that decision on whether you really need to shop online, or whether it could be obtained in the Republic of Cyprus."