Listed below are recommended bizhub fax kit settings.
Before implementing these settings, it is recommended to upgrade the MFP firmware to the latest version of firmware and verify that the bizhub fax kit also has the latest available firmware installed.
These settings are performed in Service Mode:

1. FAX Settings  Communication  Protocol set "ON" for the "V8/V34 Protocol" Protocol and set "OFF" for all other faster protocols.
2. Set “-15dBm” for all TX ATT of the following- FAX Settings  Modem/NCU  TX ATT  PIX TxATT- FAX Settings  Modem/NCU  TX ATT  Tone/Procedure Signal TxATT- FAX Settings  Modem/NCU  TX ATT  CED/ANSam TxATT
3. FAX Settings  Communication => Others we have set "OFF" for the "ECM Function"- Turning off ECM may cause the fax transmission speed to be unacceptably slow.

It is recommended that ECM be turned off as a last resort.Recommendation: Try setting 1 and 2 (above) before 3.