Brother MFC-8420 User Manual page 359

Select the "Print to Following Port" as illustrated above, if Brother
LPR Port is listed for your MFC you can just specify for Brother
Network Fax to use this previously installed port. If you have multiple
Brother LPR ports please ensure that you select the correct port
address. If in any doubt please contact your Network Administrator.
If the installer screen does not appear automatically select
Start, Run and type X:/setup.exe
(X:/ should be the drive letter of your CD ROM drive on your PC).
20 - 5 BROTHER NETWORK PC-FAX SOFTWARE