Should incoming fax lines into RingCentral ever result in a busy signal? How many lines are open for incoming faxes to a particular number?
I've never heard of RingCentral implementing any limit on number of simultaneous calls. However, I am sure there are limits at some point. Do you think you are getting dozens or hundreds of simultaneous inbound faxes? Has anyone who reported this shown you that their fax reported busy specifically as the reason for transmission failure?