Is it possible to do a domestic transfer of funds between a domestic Bangkok Bank branch to the HSBC branch in Bangkok via ATM. I don't know if HSBC is treated like a domestic bank such as Siam Commercial, Kisikorn Bank, etc. I've routinely done ATM transfer between Thai banks to pay for bills and services, but never to HSBC.

HSBC (RIP) is no more.

There is no longer any HSBC presence in Thailand. They shut down all operations last year. So to answer your question; No, it is not possible to do a domestic transfer from Bankok Bank to HSBC.

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