Royal Mail has warned of potential service delays across more than 100 UK postcodes due to poor weather and staff sickness.
The company has listed 38 delivery offices which could be most affected by a slower service.
A spokesman for Royal Mail said "adverse weather, including storms Goretti, Ingrid and Chandra in January, alongside higher-than-usual sick absence, has caused some short-term disruption to certain routes".
The firm added: "We want to reassure customers that the vast majority of mail is delivered as planned and understand how frustrating it is when post does not arrive as expected."
Royal Mail serves nearly two million postcodes and is required to deliver mail six days a week.
Regulator Ofcom last year gave the go-ahead for Royal Mail to scrap second class letter deliveries on Saturdays and change the service to every other weekday.
It launched the changes across 35 delivery offices as a pilot, but has yet to expand this nationwide across all 1,200 sites after failing to reach an agreement with the staff union.
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It is currently embroiled in a month-long dispute resolution process with the Communication Workers Union, with the aim of reaching an agreement over how the workforce will be impacted by the overhaul.
The list of the "most impacted" delivery offices and postcodes, as released by Royal Mail, is as follows:
Aberdare DO (CF44, CF45)
Ashington DO (NE22, NE62, NE63, NE64)
Banbridge DO (BT32)
Beverley DO (HU11, HU17, HU18)
Brechin DO (DD9)
Brierley Hill DO (DY5)
Chichester DO (PO18 - PO20)
Chipping Norton DO (OX7)
Daventry DO (NN11)
Glasgow G15 DO (G15)
Glasgow G52 DO (G52, G53)
Helston DO (TR12, TR13)
Hull Central DO (HU1-HU3, HU5, HU9, HU12, HU19)
Hyde DO (SK13, SK14, SK16)
Kingswood DO (BS15, BS30)
Kirkcaldy DO (KY1 - KY3)
Leicester East DO (LE2, LE5-LE7)
Lichfield DO (WS7, WS13, WS14)
Lisburn DO (BT26-BT28)
Lochgelly DO (KY5)
Lutterworth DO (LE9, LE17)
Maida Hill DO (W9)
North Tyneside DO (NE25-NE30)
Oxford East DO (OX3, OX4, OX33, OX44, OX49)
Penarth DO (CF64)
Pendle DO (BB8, BB9)
Pontefract DO (WF7, WF8, WF9, WF11)
Pontyclun DO (CF72)
Prenton DO (CH43)
Shrewsbury DO (SY1-SY5)
Sileby SPDO (LE12)
Sleaford DO (NG34)
South Shields DO (NE33, NE34)
Sunderland DO (SR1-SR6, SR9)
Swan House DO (LE1, LE3, LE7-LE9, LE19, LE95)
Swindon DO (SN1, SN2, SN3, SN6, SN25, SN26, SN38, SN99)
Waterlooville DO (PO7-PO8)
Whitwood DO (WF6, WF10)
(c) Sky News 2026: Royal Mail warns of service delays - here are the postcodes affected
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