Objective
Provide guidance for diagnosing and resolving fax failures on a Grandstream ATA HT801 that is registered and online but experiences inbound/outbound fax issues after relocation
Applies To
Grandstream HT801 ATA
Analog fax devices (e.g., Canon imageCLASS MF615iF)
8x8 PBX extensions configured for fax
Scenarios involving device relocation or environment change
Procedure
1. Extension & ATA Configuration Review
Verified extension xxxx configuration:
✅ Primary DID correctly assigned: xxxxxxxxxxx
✅ Codec: G.711u
✅ Fax Mode: T.38 enabled
✅ Call Waiting: Disabled
✅ Dial Plan: NANP-INTERNATIONAL (or whatever service needed)
✅ No restrictions applied
✅ ATA registered and online
Result: No configuration issues identified
2. Root Cause Identification
Further review identified:
Call forwarding rules were not configured
Extension was expected to forward on No Answer / Busy (rejected), but forwarding was unset
Extension profile contained over 100 voicemail entries, exceeding recommended limits and needed deletion
These conditions caused unpredictable call handling, directly impacting fax call completion.
Additional Information
Fax issues can be caused by PBX-level call handling, even when ATA and codecs are correct
Excessive voicemail entries can affect call processing
Always review:
Call forwarding rules
VM count on fax extensions
Extension behavior after relocation