Digital Fax emails not coming into Zoho Desk

Digital Fax emails not coming into Zoho Desk

We recently set up an account to receive faxes via email with freepbx.pbx. When faxes come in as a pdf attachment to our email address and is forwarded to our zoho desk account - nothing shows up. We even tried sending directly to zohodesk.com address and it was not received. Please advise.