People will continue receiving Christmas cards and parcels posted from abroad throughout January, An Post says.
It comes amid a continuing impact to international delivery services due to COVID-19 restrictions and lockdowns.
The recent cold weather has also impacted delivery in some local areas.
However, An Post says international letters and parcels will continue to be delivered 'as soon as they are received' in the country.
In a statement, they said: "Widespread COVID-related restrictions and local lockdowns across the world continue to impact the distribution and delivery of international parcels and letters.
"The number of international flights continues to be severely impacted by the COVID crisis, with only limited space available for international letters and parcels. As a result, many items posted in Ireland during December for delivery across the world are still in transit through airports and sea ports.
"Also, local delivery depots across the globe have been impacted by COVID, while some areas are also dealing with severe winter weather conditions."
Recent weeks have also seen some delivery services experience delays due to Brexit, with DPD temporarily halting its UK to Ireland deliveries due to 'extra pressure' on their turnaround and transit times.