Our Samsung Pro Xpress M3870FW was not sending faxes.
The Error showed Comm Error, Error with fax line. Though we had tried everything with our fax line and asked our provider if there was a problem with it.
Eventually I got in touch with Samsung and found some of these multi function printers M3870FW had shipped with faulty firmware.
So by updating the firmware it should sort this problem, and it did!
There was a problem in the firmware ZIP file provided by Samsung where there was no EXE file(usblist2) in the ZIP which it asks you to use. So I found the USBLIST2 on the web and got the firmware installed.
Right now there are no more problems! I thought it would be handy for anyone who had the same problem. So I have provided the updated firmware WITH the exe that Samsung has forgotten to put in the original ZIP.
I have also created a BAT file in the ZIP called RUN THIS EASY so all you have to do it connect your printer via USB cable then run this file.
Firmware version M337x_387x_407x_V4.00.01.27