The reduction in the number of flights, and flight capacity, due to the Covid-19 pandemic has led to a delay in post making its way to letter boxes in Ireland and across the world.
An Post delivered 3 million items a week in December 2020, triple the number of items delivered the previous year, but restrictions to contain the virus have had an impact.
"One of the main things is to do with flights," explained Anna McHugh, Head of Communications with An Post.
"There are so few flights. We have less than 10% of capacity that we need to get out directly from Ireland.
"We have a good subsidiary in the UK that we can use. We have good relations across the world but we know that there are items that were posted here that got out through Europe, through Asia, that are still finding their way to addresses," she added.
The same is true of parcels for delivery in Ireland, but An Post has assured that Christmas cards and parcels will find their way to recipients before the end of January.
Weather is a factor this time of year, most notably in Spain which is covered in snow, and across parts of Canada and the US.
"That's a seasonal thing and I think the postal industries would be fairly used to that," Ms McHugh said.
Another reason for delayed Christmas cards is under paid mail. "We have customers receiving Christmas cards maybe from the UK with a second class stamp on them and they trundle in at some stage, maybe late January, and that always causes a bit of a surprise.
"Apart from those, the delays are really to do with Covid, and the air capacity and space on planes. We've got to queue up, wait for space and that happens on every part of the journey for all postal services right across the globe," Ms McHugh said.