Ofcom, which fined the company £5.6m for the same failure of its regulatory obligations last November, said Royal Mail took "insufficient and ineffective steps" to improve its performance this year.
Under the regulator's rules, Royal Mail must deliver 93% of first-class mail within one working day of collection, and 98.5% of second-class mail within three working days of collection.
Ofcom's investigation found that in the year to the end of March the company delivered only 74.7% of first-class mail on time, and 92.7% of second-class mail.
The company blamed its poor performance on its "challenging financial position", and delays to the ballot on a deal that followed last year's industrial action.
"We do not consider either of these to be justifiable reasons for Royal Mail's failure to provide the levels of service expected of it," said Ofcom.
"Ultimately, it is for the company to manage its financial position taking account of its obligations. Royal Mail took insufficient and ineffective steps to try and prevent this failure, which is likely to have impacted millions of customers who did not get the service they paid for."
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Denne historien er fra December 14, 2024-utgaven av The Guardian.
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Real Madrid take aim at Uefa in bid to revive Super League
Real Madrid have spelled out their commitment to a restructuring of the Champions League in which the clubs not Uefa are in control - essentially a European Super League 2.0.
United's big reset
Rashford faces cut-price exit as part of club's cultural reboot
England get horror draw with France, Netherlands and Wales
England, the holders, have been drawn in a group with France, the Netherlands and their neighbours Wales for the 2025 Women's European Championship in Switzerland.
Maguire in 'really positive' contract talks with United
Harry Maguire is discussing a new contract with Manchester United that would commit him to at least a seventh and eighth season at the club.
Unal's fabulous free-kick earns Bournemouth a point
Bournemouth simply do not know when they are beaten. The substitute Enes Unal powered an unstoppable free-kick into the top corner, seconds after West Ham snatched an unlikely lead courtesy of a contentious penalty.
'I'm at a turning point - now it's about me playing to see how far I can go'
Emma Raducanu was hit by injuries but now feels she has the setup to be able to enjoy life both on and off the court
Filer brings the thunder after lightning halts Proteas
England will go into day three of the Bloemfontein Test in a commanding position, after bowling South Africa out for 281 and increasing their lead to 145 by stumps.
Stokes' latest injury scare adds to England's bad day
On a day in Hamilton that was already foreboding by way of leaden skies, England's troubles deepened well beyond their bleak position at stumps.
Fury vows to focus on Usyk and cut back showboating
When I look in the mirror I don't see a quitter,\" Tyson Fury says as, having suffered the first defeat of his professional career in a dramatic world heavyweight title fight against Oleksandr Usyk in May, he is about to step back into the fire of their rematch this Saturday night in Riyadh. \"I see a man who would do anything to keep going. If I get knocked down nine times, I'll get up 10. If I didn't want to do that, I wouldn't be a boxer, I'd be doing something else, like playing darts. But this is my job.\"
Athletics has funding cut by £1.75m for LA Games buildup
UK Sport has denied putting UK Athletics on the \"naughty step\" after slashing its funding for the Los Angeles Olympic cycle by nearly £1.75m.
