With our partners who forward numbers, we have extremely limited to no ability to troubleshoot or resolve certain inbound issues because of the lack of visibility and control we have in this scenario. When you experience an inbound issue, we suggest testing by having the sender send a fax to a number directly with Documo.
Note: You can do this by provisioning a new number to your account through the numbers screen.
If that test resolves the issue then the issue likely lies with your origination carrier. In certain instances, we've seen degraded quality with all of our partners who utilize Bandwidth for their underlying carrier. We have tried working with Bandwidth directly to help resolve but they very clearly state that they do not support fax on their network and it's a best effort basis. This basically means if it works that's great but they do not provide resources to troubleshoot and their network is missing some very key components necessary for reliable fax (i.e. supporting ECM - error correction mode). Because of this, we have suggested to partners seeing trouble numbers from Bandwidth that they port them directly to Documo, or they look to use another provider on their side (we can make recommendations).
Some providers choose to control their own numbers and forward the call traffic to us via SIP. The problem with that is if something goes wrong at the telephony level - we can't see it. We can't see the call-path or pull PCAPs. We can’t make a routing or configuration change with the number; we’re limited on what we can do if some specific number is having problems - it’s typically something that needs to be resolved at the carrier level.