The attack is believed to have already left more than half a million letters and parcels stuck in limbo, according to reports last week.
The attack is suspected to have come from a Russian-linked ransomware gang called Lockbit, though this is yet to be confirmed.
Here’s how the attack is affecting postal services, and when Royal Mail says it will be fixed.
How is the cyber attack affecting post?
Royal Mail is continuing to ask customers not to post items overseas while it investigates the cyber attack.
The company said it was experiencing “severe disruption” to its international export services and is temporarily unable to dispatch items abroad.
A Royal Mail distribution centre in Northern Ireland revealed its printers began “spurting” out copies of a ransom note on Tuesday, saying “your data are stolen and encrypted”.
In a statement issued on Monday, Royal Mail said: “To support faster recovery when our service is restored and to prevent a build-up of export items in our network, we’re asking customers not to post international items until further notice.”
“Items that have already been dispatched may be subject to delays.”
The company has been hit by disruption in recent months, with postal workers staging walkouts in a long-running dispute over jobs, pay, pensions and conditions.
It has caused havoc for businesses who rely on the delivery services, with major retailers such as Moonpig, Card Factory and Asos partially blaming the strikes for a drop in sales towards the end of 2022.
When will the cyber attack be fixed?
Simon Thompson, chief executive of Royal Mail, told a parliamentary select committee on Tuesday: “We’ve confirmed that we’ve had a cyber attack.”
He was unable to provide a date for when the issue will be resolved, telling MPs: “The team have been working on workarounds so that we can get the service up and running again.”
He added there would be “more news to share” soon.
Mr Thompson said he could not discuss any details of the attack, saying it would be “detrimental” to the ongoing investigation.