FAX Prohibited destination

There is indeed a setting. 

Visit:  Setting up the International Calling feature as an administrator

I sent a fax last week to a 855 number successfully and today tried to do the same thing with the same number and the error I got was that international numbers were not permitted. I about pulled my hair out.  So, after 45 looooong minutes, I sent it with a 1 in front (1855xxxxxxx) and it finally sent it. I can't tell you how frustrating this was. I'm so disappointed.