This Christmas has been a turbulent time for parcel deliveries as Royal Mail workers took strike action before the holiday.
Walkouts at the busiest time of year - caused by disputes over pay and working conditions - meant last posting days in time for Christmas were brought forward by the postal company.
What's more, some households will have missed their deliveries due to simply not being home. If you were left waiting for a parcel that never came, you most likely received a four digit code that most people would prefer not to get.
The combination of strikes and busy festive schedules mean that many parcels were branded with a code as they failed to reach their destination.
If a parcel is undelivered, it is then labelled with the code P739 by Royal Mail. If you get a card with this sequence through your post box, you will have to pick up the item from the sorting office, the Liverpool Echo reports.
This can be rather inconvenient as it can mean having to wait until the office's next opening business hours, depending on when you learn of the missed delivery. However, you can organise a re-delivery in certain circumstances.
Last year, one postal worker vowed not to deliver mail to a resident after they left a ranting note accusing him of "pretending" to ring their doorbell with a parcel.
The postman adamantly denied the accusation, and a Royal Mail spokesperson at the time said: "Every single item of mail is important to us. Our postmen and women work extremely hard to deliver to mail to customers across the country, six days a week, in all weathers."
They continued: "Thankfully the vast majority of items are securely delivered to customers, but if we believe a customer is not at home, we will attempt to deliver the item to a neighbour and leave a card.
"If we can't deliver to them, we'll leave a card and take the item back to the Customer Service Point where customers can either collect it or arrange a redelivery.
"We would advise anyone who has delivery concerns can contact the Royal Mail customer service team."
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