kumomta/docs/reference/message/get_all_headers.md

message:get_all_headers()

Gets the all the headers, decode the values to UTF-8 and return them in a lua array style table of tables:

local headers = message:get_all_headers()
assert(headers == {
  { 'Subject', 'The Subject' },
  { 'Date', 'Sun Feb 26 02:45:02 PM MST 2023' },
})