July 10 (Reuters) - Britain's media regulator said it

had set new minimum acceptable delivery deadlines for Royal Mail

to prevent long delays, and changed some existing delivery

targets that could help the postal service save up to 425

million pounds ($578.3 million).

Royal Mail, which has been trying to transform and modernise

its business as it shifts its focus to parcels, has been fined

roughly $20 million over the last two years by Ofcom for failing

to meet delivery targets.

Royal Mail must ensure that 99% of mail is delivered no more

than two days late, while delivery targets for "First Class"

mail have been cut from 93% to 90% delivered next-day and for

"Second Class" mail from 98.5% to 95% delivered within three

days, Ofcom said on Thursday.