The Post Office has announced the first 180 branches chosen for closure under plans to shut 2,500 by the end of 2008.
Some 58 branches have been earmarked in Kent, 77 in the East Midlands and 45 in the East Yorkshire area.
Another 35 branches could be replaced by "outreach services", such as mobile offices or services in shops and pubs.
Ministers say cuts are needed as the network has been losing £4m a week. A six-week public consultation is being held before final decisions are made.
Consumer watchdog Postwatch said closures were bad news but it accepted the current network was unsustainable.
The government said four million fewer people were using the current 14,000-strong network each week than two years ago, and losses had risen from £2 million a week in 2005 to £4 million a week last year.
It also pointed out that, on average, fewer than 16 people a week used the 800 smallest rural post offices, at a cost of £17 per visit to the taxpayer.
The government decided in December that 2,500 closures were required because of the Post Office's losses.
It said at the time that it wanted to help the Post Office modernise, restore profitability in its main offices, invest in new products and look at innovative ways to deliver services.
On Tuesday, the Department for Business, Enterprise and Regulatory Reform said it would provide funding of "up to £1.7bn until 2011 to continue to support the network" and to enable the Post Office "to modernise and rationalise".
Post Office managing director Alan Cook said taking the decision to close any branch was always "very difficult".
"Post Office Ltd's aim is to continue to provide essential services and support retail businesses and the local economy in as many communities as possible, subject to the very strict minimum access criteria set by the government."
Postwatch chairwoman Millie Banerjee said it was better to plan ahead for closures.
"It is now vital that the programme's overall outcome is the best possible for customers," she added.
"That means customer confusion and inconvenience must be minimised, both in terms of the branches proposed for closure and in the consultation process being meaningful and accessible to all."
Martin Bailey-Dalton, who owns one of the threatened branches in Beverley, East Yorkshire, told BBC News 24 that he was "angry and shocked" to be on the list.
"Angry for the community - it's the lifeblood of this community - and shocked because with being such a busy Post Office we do on average transactions of about £160,000 a week, which, by any stretch of the imagination, is quite a lot."
Dr Stuart Burgess, chairman of the Commission for Rural Communities, urged people to use the consultation period to make their views known about the planned closures.
He said: "Wherever there are possibilities, as part of the consultation process, to consider alternative ways of providing service, I am confident rural communities will make the most of the opportunity to come forward with practical and creative solutions."
But Gordon Lishman, director general of Age Concern, claimed the short six-week consultation period indicated "decisions may have already been made".
"We know that the vast majority of older people consider their post office to be a lifeline, with many relying on the post office as a one-stop shop to access cash and benefits, pay bills, get advice and information, and socialise," he said.
"This lifeline must not be severed."