In Outbox right click the stack you want to setup printing from and choose Stack options.
Mark Print freight letters on transmit.
Mark Print all freight letters on - And choose a global A4 printer. Use this method if all freight letters must be printed from the same printer or if you have setup scheduled transmit of EDI data.
Or mark Display the print dialog - Choose this if you want to print freight letters from various A4 printers and use manual transmit of EDI data.