How can I select a specific port to use when sending faxes?

The current FF420 firmware lets you set "Fax Direction" for each modem/port on the Modem Config page of web configuration.

"Fax Direction" is set to "Both" for all ports, by default. This means all ports are capable of both sending and receiving faxes.
You may set ports in Inbound Only or Outbound Only, which means they would only be used for receiving or sending faxes respectively. However, there is no way currently to
select a specific port from the available Outbound or Both ports to use for send fax.

If, however you set "Fax Direction" to "Outbound" for Modem 1 and "Inbound" for Modems 2 through 4, then all outbound faxes will use only modem/port 1. Inbound faxes would use remaining ports 2 through 4 only.