Westpac subsidiary BankSA will close 20 of its 104 branches and has told customers they will have to use Australia Post for over-the-counter services.BankSA said in a media release that more than 95 per cent of all BankSA transactions now take place outside branches.The bank has formed a partnership with Australia Post that will give customers access to 300 Bank@Post locations in South Australia.A BankSA spokesperson said there was a Bank@Post branch in each of the 20 locations where BankSA was closing branches. There are no Westpac branches in any of those locations.Bank@Post services include deposits, identity checks for new customers and account balance inquiries.BankSA is also developing a service called Bank Local that involves working with local government to provide agency banking services.The first of those services will be launched in Orroroo in the state's mid-north. The spokesperson said the bank was in discussion with five other South Australian councils.Westpac has been the most aggressive of the big banks in restructuring its branch network. The total number of Australian branches was cut by eight per cent to 772 during the year to September.Westpac is also shrinking individual branch footprints. Thirty-six per cent of Australian branches have been converted to a "smaller, more interactive" format.Ninety-nine per cent of Westpac branches have installed Connect Now, delivering video access to business specialists.BankSA will invest A$30 million over the next two years refurbishing branches and upgrading their technology.It is not all one-way traffic. Bank of Melbourne got 12 new branches over the past year.