As temperatures continue to struggle to rise above freezing, Royal Mail has apologised to customers in Wales for delivery delays because of the weather.
Much of Wales endured sub-zero temperatures on Tuesday, rising to just 3C (37.4F) in Cardigan Bay.
Tony Baxter, Royal Mail operations director, said they were delivering to most addresses, except some on high ground and in rural areas.
It was "simply not currently possible" to deliver mail in some cases, he said.
"We apologise to those customers who have experienced delays," added Mr Baxter.
Measures had been put in place across the UK to ensure deliveries reach people as quickly as possible, he added.
"We are advising customers to post and order early to help us deliver in time for Christmas," said Mr Baxter.
Tuesday began with a severe frost after temperatures dropped to as low as -14C (7F) in mid Wales on Monday night.
Western parts of Wales saw wintry showers with a mix of rain, snow and sleet, with Anglesey worst hit.
Drivers have been urged to take care of icy roads once again making roads treacherous.
Flights at Cardiff Airport resumed on Tuesday morning after cancellations on Monday because of freezing fog.
The coldest temperature overnight was reported to be -14C (7F) at Tirabad near Llanwrtyd Wells in Powys.
The cold is expected to last into Wednesday, before north-westerly winds on Thursday and Friday cause the snow to melt and bring temperatures back up to 7C (45F) or 8C (46F).
Drivers were once again being warned about icy roads as temperatures struggle to get above freezing.
In south-east Wales, there were also warnings of fog on both Severn crossings.
First Cymru buses said icy roads were affecting some services in the Bridgend and Maesteg area.