Though not sure but have tried the following:
In your online portal account, under Notification section of user, you will have the option to select Notification with email and not selecting any other option will avoid other notification type. example deselect notification by SMS. That might help you.
Have you tried that?
I am having the same issue. Its ridiculous because we get between 50-80 faxes a day and my yealink wireless phone cannot be filling up every 2-3 days. Something must be done from the engineering team where it gives us the option to disable this if we want! How can I escalate this to the engineering team to work on it fast. I get tired of having 40-50 voicemail messages on my phone. And in between the those messages, we have real messages that patients leave us so I have to comb through every single message to filter out real messages from these notifications of faxes. This is CRAZY!!