Lines of smtp2tg.toml.example from check-in 28fde40f7a that are changed by the sequence of edits moving toward check-in 2158b44929:

                         1: # Telegram API key
                         2: api_key = "YOU_KNOW_WHERE_TO_GET_THIS"
                         3: # where to listen on (sockets are not supported since 0.3.0)
                         4: listen_on = "0.0.0.0:25"
                         5: # whether we need to handle unknown adresses
                         6: # - relay: send them to default one
                         7: # - deny: drop them
                         8: unknown = "relay"
                         9: # default fields to show in message header
                        10: fields = [ "date", "from", "subject" ]
                        11: 
                        12: [recipients]
                        13: # there should be default recipient, get's some debug info + mail that we
                        14: # couldn't deliver (if enabled)
                        15: _ = 1
                        16: # make sure you quote emails, as "@" can't go there unquoted. And by default
                        17: # we need FQDNs
                        18: "somebody@example.com" = 1 # user id's are positive
                        19: "root@example.com" = -1 # group id's are negative
                        20: 
                        21: # to look up chat/group id you can use debug settings in Telegram clients,
                        22: # or some bot like @getidsbot or @RawDataBot